Development of a Wizard hero from the Haven faction.

You will have to start the campaign again and then choose a mage hero.
Step 1:

Step 2:

Klivren, thank you very much for the information; I didn't know that you could change the specialization at the beginning. I was already on the last mission of the campaign... I think it's still more interesting to play as a mage for the Haven faction, because both the sprites and the novices attack with light magic.