The exit is on the first level, to the far west. If you found and activated the 3 ancient pyramids (triggering a guardian skeleton of some type for each), it would activate the teleporter pad in the centre to get you to the exit. You can also just head west, though.
For Cyrion, you can apparently toss chicken meat on the ground to distract him briefly, so you get the first couple hits in.
Warriors can drink a shadow potion and use their spin attack near (but not directly on) a creature, to hit it without turning visible. Burning Wall would probably be effective, or Blind / Hell Spikes.
For the chest, drag the skull on top of the chest into your inventory and try again.