It seems impossible to reach level 50, unless you visit 50 Wisdom Trees in a row or play in the arena.
In campaigns, it's quite achievable. I managed to reach the maximum level, which is 70. This hero possessed all magic skills except for Haven. Instead, he had Tactics.
Here's what he could do:
- Disintegrate: 2816 damage
- Chain Lightning: 2048
- Suffocate: 2304
- Lightning: 1792
- Fireball: 1280
- Armageddon, Inferno, Fireball: 1024
