At the end of the game, you can choose between the "puzzle" and the "action" ending. However, all walkthroughs and videos I found only contained solution for the "action" path, but I think that the "puzzle" version is more enjoyable and contains a (slightly) better and more detailed ending. I thought it might be useful to include a solution here for that path:

In this version - just like in the "action" one -, you have to get rid of the two priests and Charles to win the game.

1. First priest: look around in the corridor, you can find objects you can move with telekinesis. Keep swinging them toward the priest, who falls behind after each hit. When you have him trapped at the end of the corridor, you get back your incineration power - use it on him!

2. Second priest: run into the corridor on the other side of the entrance hall. There is a pentagram on the floor, if you're standing in it, you can use all your powers. You have to hit the priest with a fireball, but it can be tricky, since he'll start to run away as soon as you step into the pentagram. You have to go after him and chase him back into the corridor, then quickly step in the pentagram and throw a fireball at him. If you manage to hit him once, he instantly dies.

3. Charles: use mind control on him in the main hall, then on the broken statue head below the chandelier. Bring down the chandelier with telekinesis.

Enjoy the ending! :)

I know this is an old post, but thank you. I didn't even know there was a puzzle ending until I played through the game myself and it's much better than the action one I witnessed through a Let's Play series.

Your information was spot on. The second priest was giving me trouble, but once I knew what to do, it wasn't too hard to lure him into the room by chasing him, but you have to be quick with that fireball.