Here's what I've discovered in my trips through the latest homage to the works of H.P. Lovecraft.
The Apocrean will help itself if it grabs you and hits you with its soul-stealing suction beam thing. I would assume its vulnerable to shadow damage, but I don't know for sure. You can break the tentacles holding a party member with gunfire, but not remedy capsules. Swords and bombs are unknown.
You get 8 tokens for either killing the Apocrean or finding a grave that has captured souls in it (I'm not sure which, my partner and I were a little busy running away from Cthulhu's gardener to get a good look, and there were so many stray shots being fired that I lost track of where the souls came from).
Graves can contain either: nothing, scarabs, or (maybe) souls.
There are a number of puzzles scattered through the plateau. You earn tokens for solving them. The ones I encountered were:
-Ruins with shadowfire you had to put out to access a button that freed souls. Solution: find water to put out the fire.
-A Grave with a lit blue candle next to it, with an unlit candle on the side. Solution: find fire, lit candle.
-A locked golden gate, with an arcane symbol on the ground next to it. Solution: Unknown, we couldn't find the key.
If you have any other information, puzzles, strategies, etc, post them here!
Take out a weapon with a damage type corresponding to the colour of a glowing spire, and a key will spawn.