Interesting idea. Cyrus hit on most of the big points I would have brought up I think: I like the idea of having to judge whether someone is in costume or is actually a monster, as a concept. Having both the threat of death, but also the cost of losing money, provides an interesting tension of going fast and also taking your time. I can imagine a future version of this game with multiple sections, where it gets harder and harder to tell as the aliens get better and better at mimicking people.
Plenty left to expand upon, but a decent demo of a concept. Thanks for all your hard work.