How exactly does enemy group spawning work? I saw monsters spawn in waves in a couple of bbs levels now and I'd love to know how to do this.

If you want, say, 3 minotaurs to spawn at once, place just one of them in the room, and in the object properties panel, change "amount" to 3. This will make 3 of them spawn at the same time close together.

This can applied to most things.

Yea I'm already using this function. But I found out how to make enemies spawn in "waves"
You just have to set up time AND nomon... silly me :P