Below, I will be listing my step-by-step method for unlocking this achievement:
As soon as you get to your base, the first thing you want to do is set up a defense and build up your
economy. Send your first two Siege tanks to the north end.
Build a Bunker at each entrance to the base, and load most of your infantry in the bottom Bunker.
Note that the southern entrance to your base needs less defense because the units have to walk much further
to get into your base. The North entrance is much more vulnerable as the enemy units from the North-east have a
straight-shot into your base.
Keep training SCVs and build a few tanks here and there. You want to get up to ~22 SCVs harvesting
minerals, 6 harvesting gas, 1 building Supply Depots, Turrets, and other structures, and 1 at each entrance of
your base to repair your tanks and Bunkers.
At the start of the game, your priority is only building up your economy and your defense.
Important: Whenever you get manual control of the drill, make sure you use it to
attack as many units as you can, even if you do not need the kills. When the Drill is attacking random
structures, that is time it is not attacking the wall. You will want more time so you can unlock this
achievement easier. It is important to slow down the drills progress as much as you can.
Make sure you are queueing up units to attack with the drill by attacking and then holding the shift key as
you select more units.
I have found that 5 Siege Tanks at each entrance to your base, 1 Bunker at the south entrance and 2 Bunkers
at the North entrance is the perfect amount of defense.
Put 1 Marauder in each Bunker as Concussive Shells slow down enemy units, making them easy kills for your
Tanks (if you bought the upgrade).
Build about 10 Missile Turrets all around the Drill and at the eastern edge of your base. These will
intercept air attacks.
As soon as you have this defense set up, start building units. You will want to build as big of an army as
you can. Keep it in the center of your base so none of the units get killed.
Get as many mercenaries as you can for your army. The mercenary Marines and Marauders are great because of
their high HP total. They are much easier to keep alive, especially with a few medics healing them.
Marauders in general will be the bread and butter of your army for that very reason; the high HP total plus
armor-piercing makes them effective versus most Protoss units. Combine that with Medic healing and you have a
good basis for an army.
Keep building up your army as big as you can. You will want to get all 12 War Pigs (Marine Mercenaries),
about 5 medics, at least 6 Siege Tanks, 5 SCVs (will talk about these later), and as many Marauders as you can
You will want a supply count of at least 150/200 (preferably 170/200 if you want it to be easy) in addition
to +1 upgrades for all your units.
Keep your defense set so you do not have to worry about Protoss attacks as you break into the Protoss
Breaking into the Protoss player's base is the toughest part. I recommend attacking the northwest
entrance. The first thing you want to do is set up all of your tanks in Siege Mode just outside of the range of
the Protoss player's buildings.
Next, build 1-2 Missile turrets (again, just outside Photon Cannon range) around your tanks.
Lift off a Barracks and bring it over top of your units.
Save the game in case your attack fails (you can load and try again if so).
Push up into the base with a few Marauders, get off a shot or two, then immediately run back to your tanks.
Your tanks will do a lot of damage to all the heavy ground, and your Missile Turrets will start attacking air
Here is the most important part: you have to use the drill to attack the big Protoss units. In particular,
use it to take out Immortals and Void Rays.
After a few back and forth rounds of jousting, you will eventually weaken the Protoss player's forces.
At this point, you can float your Barracks over the Protoss player's entrance and start picking off the few
Photon Cannons around the perimeter.
It is very difficult to pull this off without first luring some Air units in to your Turrets.
As soon as you kill most of the Protoss player's units, push into the main base with all of your offensive
units (still should be about 6 tanks, 5 medics, a dozen marines, 2 dozen Marauders, and some SCVs.
As soon as you get into the Protoss player's base, hold the entrance and set up your tanks in Siege
It is completely acceptable if your tanks kill a few buildings as you establish your position in the
Protoss player's base. Once you are inside, you can easily kill 50 buildings, so do not worry about the 50
kills just yet.
Stand around the entrance to the base and slowly clear out the left-hand side. Killing the Gateway and
Robotics Facility on the left-hand side will reduce the amount of units you have to fight by a significant
Build a few more Missile Turrets and slowly inch your army east across the Protoss player's base. Use the
Drill to kill buildings. You should be able to hit the target amount of 50 quite easily this way.
The most important thing here is to just take your time building up a very large army before you go in. If you go
in with a smaller army, you will get killed very easily.
Yippee-Ki-Yay... Video Walkthrough
Here is a video guide that shows how you can use the Laser Drill to easily take out the Protoss player, even
without any air units.
Other Achievements and Research
The other achievement as this level is the Drill Hard achievement. You will unlock this easily
as you work on the Yippee-Ki-Yay achievement.
The research locations are marked on the map. You can use the drill to blow up the Xel'Naga buildings and then
grab the relics. You can easily fight to these buildings with a small army of 6 Marauders and 2
Starcraft 2 Yippee-Ki-Yay Achievement Conclusion
By following these steps, you should be able to easily beat this mission without a problem. The key points are
to use the drill to attack units purely to slow down the timer, mass a large army, bust into the northwest base,
then slowly kill off the Protoss player's buildings.