Robot Entertainment (the studio behind Orcs Must Die!, Hero Academy, and, of course, the co-op tower defense/action RPG hybrid Orcs Must Die! 2) turns four years old this weekend! Congrats, guys! To celebrate, they're running a massive 75% off sale on their games and DLC. During this weekend, you can pick up Orcs Must Die! 2 for a mere $3.74 through their store! It'll provide you with a code that you can redeem through Steam (note that Steam itself is not offering this sale, so you'll have to go through the Robot Entertainment store for the discount).