Starcraft 2 Research, Armory Upgrades, and Mercenaries Guide

Starcraft 2 Strategy Guide --> Starcraft 2 Campaign Guide --> Starcraft 2 Credits, Research, & Armory Upgrades guide (you are here)

Discover the best way to spend your credits and research points in the Starcraft 2 Wings of Liberty Campaign

One of the most important things players can do in order to make the campaign easier is to choose the right research, armory upgrades, and mercenary hires.

In this guide, we will discuss not only what the best choices are, but why you need to make these choices and how you can apply these upgrades and technologies to make clearing the game easier on brutal mode.

Protoss Research Guide

Players must choose 5 of the 10 new technologies available from collecting Protoss technology (one from each level). Here are the choices:

5 Protoss Research Points

• Ultra-Capacitors - Weapon Upgrades (i.e. +Weapons at the Engineering Bay or Armory) also increase attack speed by 5% per level.

• Vanadium Plating - Armor Upgrades (i.e. +Armor at the Engineering Bay or Armory) also increases life by 5% in addition to increasing armor.

While it does not make a big difference either way, I think that the Ultra Capacitors are the real winner. The reason for this is that on the All In mission (by far the hardest mission on Brutal), most of your units actually end up in Bunkers while automated defensive buildings tank most of the damage. Units in Bunkers as well as Siege Tanks hidden at a safe distance do not benefit from extra health, but extra attack speed benefits all units.

Vanadium Plating is good however for previous missions, particularly if you are using bio. Marines with over 60 HP backed up by Medics are very hard to kill.

10 Protoss Research Points

• Orbital Depots - Supply Depots are built instantly (they are summoned from the sky).

• Micro-Filtering - Refineries and Automated Refineries produce vespene gas 25% faster.

Both of these upgrades are good, though I think the better of a player you are, the more benefit you get out of Micro-Filtering. Gas is the limiting resource at most maps, and this actually lets you get more gas (leading to more units) that you would otherwise not be able to get. This is particularly noticeable during the All-In mission on Brutal mode, particularly if you are making heavy use of Banshees (ground version) or Ghosts (air version).

With that said, Orbital Depots are still good. You can create walls instantly, but this is not as practical as you might imagine versus the computer (as opposed to Multiplayer). It does save building time, but with better planning the saving of time is not that important.

15 Protoss Research Points

• Automated Refinery - Refineries automatically harvest gas with no SCVs.

• Command Center Reactor - You can produce 2 SCVs at once from a single Command Center.

At first, both of these seem really good, but the truth is that Automated Refinery is 100x better. There are multiple benefits of choosing the Automated Refinery over the Command Center Reactor.

The first and primary benefit is that it lets you start getting Vespene Gas early on in the mission. You can use your SCVs to build Refineries the second the mission starts and it is like having an extra 3 SCVs instantly per refinery.

Additionally, since you do not need SCVs on each gas, you save 3 supply and 150 minerals each time you build a Refinery. This really comes in handy on missions like All In, where you can easily hit the supply cap. The extra 9 supplies that would be dedicated to gathering gas can instead be dedicated to 9 supply worth of units to fight the enemy with.

As a final benefit, you can take a "gas expansion" without actually building a Supply Depot. If there is a vespene geyser, you can build a refinery on it long before you get a Command Center there (if at all) and it will continue to harvest. This is noticeable on any mission where you need extra gas but not minerals (i.e. Supernova).

The Command Center Reactor has an easy replacement as well if you want extra SCVs - building another Command Center. You can build an Orbital Command that in a very short amount of time with the Advanced Construction armory upgrade. This will then pay for itself in just 2 MULEs and then you have double SCV production.

20 Protoss Research Points

• Raven - Gives players access to the Raven. This is a detector unit with auto-turrets, Point Defense Drones, and Seeker Missiles.

• Science Vessel - Gives players access to the Science Vessel. This is a detector unit with the ability to heal mechanical units and use Irradiate.

The Science Vessel is better (no contest) than the Raven for the Campaign. It is the only unit that can heal mechanical units for no resource cost and it has the added benefit of being able to fly. This means that it can be used for flying armies to have the same effect as Medics do in bio balls.

The Science Vessel, due to its ability to fly, can also reach units for repairs that SCVs might not be able to get to, such as a cluster of Siege Tanks that might be unreachable. The Science Vessel can also repair SCVs.

Irradiate is surprisingly useful as well. It is a very cheap ability that can be used to kill Mutalisks, Hydralisks, and Zealots with ease. It works best when placed on a very large unit like an Ultralisk.

25 Protoss Research Points

• Tech Reactor - Combines the functionality of the Tech Lab and Reactor into one add-on.

• Orbital Strike - Barracks units now arrive by drop pod and can be summoned anywhere on the map.

Without a doubt the Tech Reactor is the best add-on here. It saves so much building space and extra resources by allowing you to produce high-tech units two at a time out of a single production facility.

It becomes incredibly useful on the toughest missions in the game because on maps like All In and Gates of Hell, your building space is limited. Getting more production out of less building space makes missions much easier.

Zerg Research Guide

Zerg Research is a little different than Protoss research in that Zerg research seems to primarily introduce new things entirely to the Terran arsenal whereas the Protoss research primarily upgrades your current units and buildings.

5 Research Points

• Shrike Turret - Outfits bunkers with an automated turret that can attack both air and ground units.

• Fortified Bunker - Increases bunker health by 150 life.

Both of these work, but Fortified Bunker is considered the better upgrade. Shrike Turret I believe is under-rated on the earlier missions, since it is a stand-alone defense on many of the earlier missions where you do not face any siege units.

However, All In on brutal mode is definitely the toughest mission in the game and Fortified Bunker is definitely the best choice for that mission, so most players will want to forgo the earlier convenience provided by Shrike Turret for the end-mission boost provided by Fortified Bunker.

10 Research Points

• Planetary Fortress - Command Centers can be upgraded to the Planetary Fortress, an automated defensive structure with extra armor and a ground-based splash attack.

• Perdition Turret - A Flame Turret that sits underground when it is not in combat (SCVs can move over top of it). It attacks with a moderate-range flame that deals splash damage.

Both of these are good, but I prefer the Perdition Turret. The Perdition Turret is really strong against Zerg units and does a lot of damage. It also builds very quickly and is inexpensive. The only downside to the Perdition Turret is that it can be outranged by Hydralisks, Stalkers, Immortals, and Colossi.

Neither building can attack air units. However, you can place a line of Missile Turrets behind a line of Perdition Turrets to solve that problem. Include a few tanks behind the line of missile turrets and they will be able to take out the ranged units that would otherwise outrange the Perdition Turrets.

The best thing about the Perdition Turret over the Planetary Fortress however is that it goes underground when it is not attacking. This makes it so easy for SCVs to repair all the turrets and it also makes it very easy to move units into and out of your base. The Planetary Fortress is bulky and immobile, so you cannot get around it once it is built.

15 Research Points

• Predator - Anti-Infantry ground unit with a melee attack that has an AoE attack. Seems to work well versus Marines and Zerglings, which limits its usefulness.

• Hercules - Giant flying transport that stores many units and unloads them nearly instantly.

Both of these units are not that good. This is easily the worst research type you come across. There is no reason to use the Predator when a ball of Marines backed up by Medics is just as effective against ground units and the Marines can also take out air units and buildings.

The Hercules is interesting but the value of drop play in single player is very low.

20 Research Points

• Cellular Reactor - Specialist Units start with 100 extra energy and have 100 extra maximum energy.

• Regenerative Bio-Steel - Mechanical units heal very slowly (36 HP per minute).

Most newbie players will pick Regenerative Bio-Steel whereas most advanced players realize that Cellular Reactor is better.

Regenerative Bio-Steel is deceptive because the healing rate is so slow that it is hardly worthwhile. At 36 HP per minute, it takes several minutes for a single mech unit to heal to full (or longer if it is a big unit like a Battlecruiser) - too long for any real usefulness.

The extra energy is very beneficial for all your caster units. Science Vessels can easily drain themselves dry from healing and can always benefit from extra healing capacity. Ghosts and Spectres can significantly benefit from the extra energy, as it lets them front load a lot of damage with Snipe or Psionic Lash right after spawning.

Finally, if you are using Banshees for the ground version of All In, the extra starting energy is awesome since they can cloak for a long time right after being built.

25 Research Points

• Hive Mind Emulator - Builds a tower which can permanently mind-control Zerg units in range.

• Psi Disrupter - Slows nearby Zerg units by up to 50% (depends on size).

This is the most important research choice you will make in Starcraft 2. The Hive Mind Emulator may not seem good at first but it is without a doubt the best research upgrade you can get and makes any mission versus Zerg incredibly easy.

The gimmick with the Hive Mind Emulator is that they are cheap to build, you can build an unlimited number of them, the mind control only costs 50 energy, and the mind controlled units are yours to keep and have no supply cost.

This means that on any mission where you fight Zerg, you can build 10 Hive Mind Emulators near where the Zerg player attacks your base, which you can then use to steal any offensive attacks the Zerg player makes. If you do this for a few attacks in a row, you will find yourself with a massive Zerg army that you can then combine with your own army to easily wipe out the computer.

You can go way over 200 supplies worth of units this way as well. On All In, it is possible to steal over 100 enemy Mutalisks and 40 Broodlords!

How to Spend Your Credits: Armory Upgrades & Mercenaries

Players can earn 2,280,000 credits over the course of the Wings of Liberty campaign. This is done by completing every mission in the game before going to Char (including the Piercing the Shroud secret mission) and collecting every single piece of research at every map (extra research points beyond 25 are converted into 10,000 credits per research point).

While this is may seem like a lot of credits, if you hire all of the mercenaries, you only have enough to research about half of the upgrades available to you in the Armory. This guide will examine both the Mercenaries and the Research choices so you can save your credits for the most important upgrades.

Mercenaries in Starcraft 2 Wings of Liberty

Before we discuss the actual mercenaries available in Starcraft 2, as a general rule of thumb, mercenaries are amazing. They give you a higher HP, higher damage unit that is produced instantly out of its own building at a resource cost not much different than regular units.

The instant production and regular supply cost of the Mercenaries though is what makes them so valuable. If you are going to max out your army at 200/200, if one army has mercenaries and the other does not, the mercenary army will be better every time due to the extra health and damage.

As a result, if you are going to use a specific unit in your army, you will want to hire the mercenary of that type. In other words, if you ever use Siege Tanks in your army, you definitely want to hire Siege Breakers. However, mercenaries for a unit type you never use such as the Goliath are a lot less useful.

Mercenary Options - What to Pick

Here is a list of the mercenaries, their cost, what they are good for, and whether or not you should spend the credits unlocking them.

War Pig - 4x Elite Marines. Unlocked for free. Can be summoned every 5-minutes in game up to 3 times. Summoning cost is 250 minerals and 4 supplies. These are given to you automatically and are arguably the best Mercenaries in the game given how frequently you will use them. They do not deal that much more damage than regular Marines, but the extra health makes them so survivable that with medic back-up they never die. On missions where you do not use bio, War Pigs are great units to put into bunkers.

Devil Dogs - 2x Elite Firebats. Unlocked for 25,000 credits. Can be summoned every 5 minutes up to two times. Cost is 250 minerals, 75 gas and 4 supplies. In my opinion these are not worth the credits because Firebats are a bad unit for the campaign. Perdition Turrets are better on defense and on offense their melee range gets them way ahead of your medics, leading to their premature death.

Hammer Securities - 2x Elite Marauders. Unlocked for 30,000 credits. Can be summoned every 6 minutes up to two times. Cost is 250 minerals, 75 vespene gas, and 4 supplies. The extra health and damage is very low for the Hammer Securities compared to other mercenaries, but they are still good. Even without the bonus health having the ability to instantly summon two pairs of Marauders in each mission would be good, so any boost in damage is appreciated and worth it. You will use these practically every mission so you definitely want to hire them.

Spartan Company - 2x Elite Goliaths. Unlocked for 40,000 credits. Can be summoned every 6 minutes up to two times. Cost is 300 minerals, 125 vespene gas, and 6 supplies. While these units get a nice health and damage boost, they are still Goliaths, and as a result, I cannot recommend them spending the credits here unless you have nothing else to use them on. The problem with Goliaths is that they are really clumsy, take up a lot of space, and die easily. They do not play well with bio balls or air units, which will make up the bulk of your offensive armies. They are really only good for defense and can be used to sit near Siege Tanks to provide them with air defense. However, Missile Turrets can do the same thing for less resources and no supplies.

Siege Breakers - 2x Elite Siege Tanks. Unlocked for 45,000 credits. Can be summoned every 7 minutes up to two times. Cost is 400 minerals, 200 vespene gas, and 6 supplies. Definitely the best Mercenary in the game as their damage is incredible. The best part about the Siege Breaker though is that you typically only need a pair of them to defend a base, and since most of your armies should be bio or flyers, having this mercenary allows you to skip over the factory entirely. You can summon these on practically every mission to play defense for you.

Hel's Angels - 3x Elite Vikings. Unlocked for 45,000 credits. Can be summoned every 5 minutes up to two times. Cost is 400 minerals, 300 vespene gas, and 6 supplies. These get a nice health and damage bonus over regular Vikings and given that you get 3 instant Vikings, it is a pretty big boost to your army's strength on an instant-click button. Definitely a worthy hire because 3 Hel's Angels can take out most air threats you actually run into during the campaign. Comes in handy during All In if you have the air version.

Dusk Wings - 2x Elite Banshees. Unlocked for 60,000 credits. Can be summoned every 7 minutes up to two times in a mission. The cost is 350 minerals, 200 vespene gas, and 6 supplies. These are really good if you opt for the ground version of "All In" as these Banshees tear up the Nydus Worms. Otherwise, you might not use Banshees that much, given that you do not unlock these until near the end of the campaign. They are also a good emergency summon if you get attacked when your army is away from your base. You should have the spare credits for them but it is not a must-have.

Jackson's Revenge- 1x Elite Battlecruiser. Unlocked for 80,000 credits. Can be summoned 1 time per mission after 7 minutes. The cost is 400 minerals, 300 vespene gas, and 6 supplies. This is a decent unit, but the 80,000 credit cost makes it a little expensive. You should have the extra credits available if you really want it, but if you made some questionable investments early and only have a limited number of resources to choose from, not getting this mercenary is a good way to cut spending.

Mercenary Must-Haves

To recap, I think that hiring Hammer Securities, Siege Breakers, and Hel's Angels are the only must-have mercenaries. This is a total credit cost of 120,000 credits. Optional hires are the Dusk Wings and Jackson's Revenge, which could take on another 140,000 credits for 380,000 total being spent on mercenaries.

Armory Upgrades Guide - Where to Spend Your Credits

There are 5 different categories of upgrades available in the armory: Base, Infantry, Vehicles, Starships, and Dominion.

Base Upgrades

The Base Upgrades is the only section where you will always want to buy every single upgrade. This will run a total of 575,000 credits, but all the upgrades are good and should always be purchased. They are:

• Projectile Accelerator - 40,000 credits. Causes units in Bunkers to gain +1 range. This is a nice upgrade because it makes units in bunkers more effective.

• Neosteel Bunker - 50,000 credits. Increases the number of slots in a Bunker by 2. This is a big upgrade because it makes the offensive capacity of Bunkers 50% higher (or more if you use Marines + Medic).

• Titanium Housing - 50,000 credits. Increases the amount of life your Missile Turrets have by 75. An easy choice for an upgrade given how good Missile Turrets are against Mutalisks.

• Hellstorm Batteries - 80,000 credits. Gives the Missile Turrets a second attack that does splash damage. This significantly boosts the damage of Missile Turrets, shredding light units like Mutalisks instantly.

• Fire-Suppression System - 90,000 credits. Terran buildings no longer burn down and will automatically repair themselves to 50% life. This will save many buildings if you do not have any SCVs nearby to repair them.

• Orbital Command - 125,000 credits. It may seem expensive, but you cannot beat the ability to summon MULEs (each one is worth 270 minerals). Scanner Sweep is nice too, but the MULEs are the real prize here.

• Advanced Construction - 60,000 credits. Multiple SCVs can be used to construct a single building, speeding up its construction time at no extra cost. This is really nice for getting up new production facilities or expanding. You can pull 8 SCVs to a new expansion and then have them all build the Orbital Command expansion there in about 15 seconds for an instant expansion. Also works well when combined with Automated Refinery.

• Dual-Fusion Workers - 80,000 credits. Causes SCVs to repair twice as quickly. This is a must-have, particularly at missions where you need a lot of repairing like All In.

Infantry Upgrades

I only recommend getting half of the upgrades of the 10 available here: Stimpacks, Combat Shield, Stabilizer Medpacks, Concussive Shells, and Kinetic Foam for a total cost of 375,000 credits. Here is the list of all the available Infantry armory upgrades:

• Stimpacks - 50,000 credits. Grants access to the Stimpack ability. This causes Marines to take 10 damage in order to move and attack 50% faster for 15 seconds. With medic support, this damage is negligible. Additionally, Marines in Bunkers can use Stim Packs, and if you place a single Medic inside the Bunker with the Marines, the Medic will heal the stimmed Marines. This is a must-have upgrade.

• Combat Shield - 60,000 credits. Increases Marine health by 10. This is a must-have upgrade as it makes Marines so much more survivable, especially since it replaces the health lost by Stimpacks.

• Advanced Medic Facilities - 60,000 credits. Causes Medics to no longer need a Tech Lab on the Barracks. This lets you make 2x Medics at a time out of a Barracks with a Reactor on it. Definitely a waste of credits though because this technology is rendered obsolete by the Tech Reactor Protoss technology.

• Stabilizer Medpacks - 105,000 credits. Causes Medics to heal 25% faster while spending 33% less energy on healing. This is an amazing upgrade and a must-have. It is so noticeable and your bio balls will live so much longer with this upgrade. You cannot beat extra output.

• Incinerator Gauntlets - 40,000 credits. Gives Firebats a 40% larger attack area. Waste of money since Firebats are terrible.

• Juggernaut Plating - 85,000 credits. Gives Firebats +2 armor. Waste of money since Firebats are worthless.

• Concussive Shells - 70,000 credits. Marauder attacks slow all units in the target area. Definitely worthwhile and you will use it throughout all the early missions and even into the late ones. This snare lets you kite with Marines/Marauders. It also makes your defense more effective if you place a Marauder or two in Bunkers in order to snare incoming enemies.

• Kinetic Foam - 90,000 credits. Increases Marauder health by 25. Definitely want to pick this up as well given that Marauders are used so frequently.

• U-238 Rounds - 60,000 credits. Gives Reapers +1 range and +3 additional damage to light targets. This is a fun upgrade to get if you want to use Reapers, but it is kind of a waste of credits in the long run as Reapers are not used much late in the campaign.

• G-4 Clusterbomb - 75,000 credits. Gives the Reaper an small charge which blows up to deal damage to ground units. Similar to Spider Mines, but honestly worse - waste of credits in my book.

Vehicle Upgrades

Most of the vehicle upgrades are a waste of credits. The only ones I recommend getting are the Siege Tank upgrades Maelstrom Rounds (105,000 credits) and Shaped Blast (140,000 credits) for a total investment of 245,000 credits.

Here is the list of available upgrades:

• Twin-Linked Flamethrower - 40,000 credits. Doubles the width of the Hellion's flame attack. Worthless since Hellions are no good in the campaign - the computer uses too many Spine Crawlers and Roaches for Hellions to be viable.

• Thermite Filaments - 60,000 credits. Hellions deal an additional +10 damage to light armor. Worthless because Hellions are worthless.

• Cerberus Mine - 50,000 credits. Increases spider mine blast and trigger radius by 33%. Sort of a waste of credits but could be a fun/interesting combo when paired with Replenishable Magazine. Definitely not needed however.

• Replenishable Magazine - 60,000 credits. Allows Vultures to train more Spider Mines for 15 minerals each. Again, this upgrade is not mandatory, but it could be useful if you want to make a few Vultures to just lay Spider Mines on defense missions.

• Multi-Lock Weapons System - 50,000 credits. Allows the Goliath to fire at ground and air units at the same time. This is a huge damage boost for the Goliath, but only if you like using Goliaths. I find them too clumsy to micro appropriately so I tend to skip this upgrade. Goliaths can be good however on air defense missions like the air version of "All In".

• ARES-Class Targeting System - 80,000 credits. Gives the Goliath +3 missile range and +1 cannon range. Once again, this is an amazing upgrade, but only if you want to use Goliaths. If you do not use Goliaths do not get this upgrade.

• Tri-Lithium Power Cells - 75,000 credits. Gives Diamondbacks +1 range. This is too expensive for a unit with little use. This however would be a really cool upgrade to have in multiplayer, but does not serve much purpose in the campaign.

• Shaped Hull - 90,000 credits. +50 max health for Diamondbacks. Diamondbacks still are not very good though for most missions and are still too fragile for the supply and resource cost in my opinion.

• Maelstrom Rounds - 105,000 credits. Causes the primary target of a Siege Tank's blast in Siege Mode to take 40 extra damage. Does not effect splash damage. This is a must-have upgrade no matter what your playstyle as it sends Siege Tank damage off the charts.

• Shaped Blast - 140,000 credits. Reduces Siege Tank splash damage by 75% to friendly units. This is another must-have upgrade as it prevents your Siege Tanks from killing off your own units and structures (with the reduced damage, medics and SCVs should be able to handle the splash damage).

Starship Upgrades

Starship upgrades are very expensive and can easily drain your credit pools if you are not careful. The only mandatory upgrades depend on what version of All In you choose. If you have the ground version, you will want both Banshee upgrades (Cross-Spectrum Dampeners and Shockwave Missile Battery) whereas if you have the air version you will want both Viking upgrades (Ripwave Missiles and Phobos-Class Weapons System). The Viking upgrades run 165,000 credits whereas the Banshee upgrades run 190,000 credits.

Here is the list:

• Rapid Deployment Tube - 50,000 credits. Causes the Medivac to unload units nearly instantly. Not worth it since Medivacs are largely irrelevant thanks to the higher output Medic.

• Advanced Healing AI - 115,000 credits. Allows the Medivac to heal two targets at once. Once again, this is a waste of credits since the higher HP/second output of the Medic is stronger than the Medivac.

• Tomahawk Power Cells - 80,000 credits. Causes Wraiths to start with +100 energy. Wraiths are not that useful so this is a waste of credits.

• Displacement Field - 125,000 credits. When a Wraith is cloaked, it will automatically dodge 20% of incoming attacks. Wraiths are still bad though so ignore this upgrade.

• Ripwave Missiles - 75,000 credits. Causes the Viking's anti-air attack to deal splash damage. This gives the Viking undisputed air superiority, as light units like the Mutalisk otherwise are able to defeat Vikings.

• Phobos-Class Weapons System - 90,000 credits. Vikings gain +2 range on their air attack and +1 range on their ground attack. This makes Vikings an anti-air siege flyer and is a huge upgrade.

• Cross-Spectrum Dampeners - 80,000 credits. Allows Banshees to stay cloaked for twice as long (halves cost of energy drain from being cloaked). Good for the "All In" Nydus worm version where you make heavy use of cloaked Banshees.

• Shockwave Missile Battery - 110,000 credits. Causes Banshee attacks to deal damage in a straight line. This is a nice damage pick-up, especially if your micro is good. Good for the Banshee on All In, but otherwise, Banshees are not frequently used.

• Missile Pods - 140,000 credits. Gives the Battlecruiser access to the missile pod ability, which deals splash damage to air units. A waste of credits since it costs energy - better off using Defensive Matrix (if you have it) or Yamato Cannon.

• Defensive Matrix - 150,000 credits. Gives the Battlecruiser access to the Defensive Matrix ability, a skill which costs energy and creates a shield that absorbs 200 damage that lasts for 10 seconds. Not bad, but kind of expensive for a unit you do not get until the end of the game. Definitely optional.

Dominion Upgrades

Dominion Tech upgrades are all decent, and I recommend getting the Ghost/Spectre upgrades no matter what (210,000-225,000 credit cost, depending on whether you have the Ghost or Spectre). The Thor upgrades are optional.

• Ocular Implants - 85,000 credits. Gives the Ghost +2 range and +3 sight. This is better than it looks because it makes the Ghost amazing when placed in a Bunker. It is effectively an anti-ground and anti-air siege unit.

• Crius Suit - 125,000 credits. Ghost's cloak no longer costs energy. This is an amazing, under-rated ability. This lets you put a few Ghosts around your base on any mission that are permanently cloaked that can defend you against anything. You can use Snipe to pick off Overseers and Scanner Sweep to find and kill Observers, at which point your Ghosts are unstoppable on defense. It also frees up energy for Snipe.

• Psionic Lash - 100,000 credits. Gives the Spectre an ability which deals 200 damage to a single target. This is a really nice skill as it lets the Spectre blow up just about any unit. You should have plenty of energy for it as well if you get the Nyx-Class Cloaking Module.

• Nyx-Class Cloaking Module - 125,000 credits. Cloaking with the Spectre no longer costs energy. As mentioned in the Crius Suit bullet point, this is an amazing ability, as it allows your Spectres to stay permanently cloaked. You can leave a few of these cloaked in your base on defense and you can defend against virtually any attack if you are quick about using Psionic Lash to take out detectors.

• 330mm Barrage Cannon - 130,000 credits. Causes the Thor's cannon attack to stun the primary target and deals area of effect damage. This is not bad if you can get it off against Kerrigan, because even though she moves while stunned, she cannot cast spells while stunned. The only downside though is that Kerrigan can 1-shot Thors with her special lifting attack and their slow movement speed makes it hard to use.

• Immortality Protocol - 140,000 credits. A destroyed Thor becomes wreckage which will rebuild itself very quickly for 200 vespene gas. This is an interesting upgrade if you use Thors and has a lot of cheesy applications considering if the wreckage is not attacked, the Thor will restore itself with full HP.

Total Cost of Mandatory Upgrades & Mercenaries

Adding up the cost of the upgrades and mercenaries that I would consider mandatory, you will need to spend 1,690,000-1,730,000 (depending on mission choices) credits out of the 2,280,000 credits you have to spend. This gives you 500,000-550,000 credits left over to spend on whatever you want - it is personal preference. This way if you accidentally pick something that is not very useful, you will have plenty of credits left over to get the things you really need.