What is the best quick way to test a mod with a monster in it? Is there a way to just spawn it, or do you have to run around a level until you find one?
Make a test room in rooms.xml (no doors, empty space, etc). Put <monster name="whatever your monster's name is" x="3" y="3" /> (or whatever coordinates you want it to appear at; remember that the upper left corner of a room is 0,0, not 1,1). Launch the game with the launch options -debug-flag -testroom "whatever your test room's name is" -x 5 -y 5 (or whatever coordinates you want to start at).
I tried this, but my game keeps crashing when I try to start a new game, right after the screens that tell about Dredmor.
That means one of your sprites isn't indexed properly or your room is improperly built. Or you're not matching the room name exactly.