Standard Price: $9.99
Sale Price: $2.49
Developed by Hopoo Games, Risk Of Rain is a bargain at 75% off. Incorporating roguelike mechanics with 2D Metroidvania sensibilities, you face off against a near-endless swarm of increasingly difficult enemies, requiring you to locate a randomly placed teleporter within each level to move on to the next.
The developers have since released Risk of Rain 2, also on offer at 20% off. Both are worth looking into, though, RoR2 replaces Risk of Rain's 2D style with 3D models and environments and is still in Early Access.