Is it possible to cahnge the value of gravity during the level? e.i. I'd like to have low gravity in one room.

I also forgot, how to put dead bodies on the map. I remember killing monsters somehow, but can't quite remember the optimal way. 

hypnotic and some other mods have triggers that set gravity on the player so you can place those triggers at all the doorways where gravity needs to change. (should be pairs of triggers so that it gets reset if you go back out.) Entities that spawn inside the room need their starting gravity set explicitly using “gravity” field on each entity.