Wooo! Very excited to finally be releasing this game - very excited to hear what you guys think. It's a paid game (our first in a while, esp. at the 2.99 price point), no ads, and I think you'll find the IAP implemented is fairly light and completely optional.
Originally Posted by sink_or_swim
There are 2 currencies, yes - Doom Shekels and Evilness. Doom Shekels are used to unlock and level-up your traps and minions. Evilness is used only for in-game power-ups. You earn a fairly generous amount of both just by playing - Evilness is gained by completing mini-goals, Shekels by completing levels and defeating heroes.
In part it's so you don't have to worry about hoarding currency of one type since they're used for different things. If Shekels were also used for in-game power-ups then you'd have to weigh using that in the heat of the moment when you're about to lose a level and being able to keep on your upgrade path.