Scrye
Lights up the area, casts glow on enemies so that you can see them better, lets you view and hear events of the past.
 

Ectoplasm
This powerful spell does as much damage as a revolver. You can kill howlers with ectoplasm while reloading the pistol.
 

Dispel Magic
Destroys magic obstacles and shields (like the ones used by Trsanti witches), removes diziness after mindshatter, kills scarrows.
 

Invoke
This is the only spell you can defeat skeletons with. It also makes some humanoids commit suicide. The second use of Invoke is resurrection of dead enemies so that they take your side for a short time, after that they disappear.
 

Haste
Lets you run faster and jump longer.
 

Shield
Creates a shield like the one used by Trsanti witches, but only in front of you.
 

Skull Storm
A really powerful spell. Lets you throw skulls which do as much damage as several dynamite sticks.
 

Lightning
You'll need it to solve a couple of puzzles. Lightning can also be used as a weapon, though it costs too much mana and takes several seconds to recharge. In combination with the speargun, charges the spears.
 

Flight
Not exactly a spell, just the ability of flying upwards into the air when pressing the "jump" button. The flight lasts not very long and is available only on the last levels of Oneiros and in Eternal Autumn.