Shroom

The Shroom is a common enemy found in survival mode. They attack the player by either punching, shooting, or throwing spikes. They are able to climb walls and crawl on the ceiling. Oddly enough, they are able to open doors although they are not tall enough to reach the door knob. Before v102 Alpha, they could only carry spikes, but now they can hold any gun/throwable (verified in the Level Editor), and they can also spawn with guns and other weapons in official Survival maps (Such as "Villa"). On an unrelated note, in Safest Gate, make sure not to crush the Shroom with the elevator; They will clog up the elevator, and annoy the living crap out of you

Spawn
As of v101 Alpha, they spawn from little, mushroom shaped houses often located on top of something (e.g. another building). In Survival House, its spawn is on the top of the spawn building. In Safest Gate, there is one spawn in the left of the spawn building, and another one in the top of the first building at the left of the spawn.