From my experience in the game...

Generally speaking:
Until you kill Boss 1, you get creatures of the forest.
Until you kill Boss 2, you get forest is moving,
Until you kill Boss 3, you get swamp smells or sulphur air
Until you kill Boss 4, you get wolf hunts or drakes
Until you get Boss 5, you get the horde or skeleton surprises

All the bosses pretty much guarantees any of the raids.

The troll raids don't happen unless you kill two or more trolls. Tried and tested in EVERY game I've played and this has been the case. Those boys are vindictive!

Biome location does have a small effect on what raids/mobs you get:

If you have a base on or near a mountain you are very likely to get drake and wolf raids more than most other things. Skeleton, swamp, sulphur, and horde raids appear to happen everywhere. Creatures of the forest and forest is moving raids only seem to be early game raids. I've never seen either again once I've downed the Eikthyr or the Elder.

I'm yet to have a cauldron raid so I am not sure what triggers that, whether it's random or tied to the boss progression.