I felt like the mana system wasn't really explained well in game; I was confused about why I sometimes couldn't do something (and didn't know what the thing about "move [x mana]" meant; I think that might have been a bit clearer if it was instead "move [1 mana per space]" or something) until I actually looked down at the description. There also seems to be a bug where if you click a spell to deselect it, the button will still appear selected.
I basically solved the first torch level pretty much by accident, and I don't know how I did it. (It's also not really clear to me what exact parts of the room are dark; I don't remember it looking different than the other levels where Donkus could see.)