DISCUSSIONS on “Rules for online games in HoMM3 and formulas for calculating player rating.”

5.10 Izra and Vidomine are allowed to continue developing the "spellcasting" skill up to the "expert" level only with the last skill offered; otherwise, they must be dismissed on the same day. If these heroes were already released from prison with "expert" spellcasting, and also if this skill was developed while they were students, then they can be used without restrictions.

Izra, level 10: +15% Necromancy (45% total)
Izra, level 20: +30% Necromancy (60% total)
Izra, level 30: +45% Necromancy (75% total)

At level 10, consider adding Necromancy boots (level 10 is reached very quickly); at level 20, equip a full Necromancy set. I often played as Necromancer and believe me, this is a huge bonus. And what if you also have Necromancy artifacts? In the late game, this means 5,000 skeletons instead of 2,000. That's game over. And if you also have a powerful Ghost. Well, you can figure out the rest yourself.