Heart of the Night

If you switch, say, from "Chaos" to "Light" on the Mentor at the end, what spells will be in the spellbook?

Gerter
Spells that have been learned once remain forever (this is a game mechanic).

The fact that the old spells will remain isn't very important. What's more important is where to get spells for the new school of magic? Presumably, nowhere. This means that it only makes sense to change the Mentor's skills to non-magical schools. The choice turns out to be not very diverse.

A lyrical digression about Greta's specialization. The Elven army is a strike force. If an Elf doesn't have the "ability to simply rush the enemy" on the first turn, then it's not the right Elf. Because on the second turn, he will lose his army. Specializing in summoning a dragon is a burden for him. If he is summoned on the first turn, 7 stacks will remain without casting, and with "Haste" and good morale (which is very good here), some stacks will already deal a couple of blows to the enemy. If you summon on the second turn, the dragon will constantly be late, and the remaining stacks will almost all be defeated without it. What is good for a Necromancer cannot be good for an Elf. Let's see what the Defender of Moriton is planned to be like. So, skills: Education (starting), Summoning (summons a dragon, fills gaps in the fortress walls), Mechanics (provides a Witch), Chaos (many artifacts for him, Daughter of Silanna - an energy channel, Presence reduces mana costs. Greta only lacks mana if she actively uses "Chaos"), Defense (given that there are many Necromancers and he needs to stay in the castle). Which character's progression does this resemble, other than an Elf? In this configuration, only "Absolute Defense" is missing.