I think it'd be nice to have more important NPCs than just wandering trader. And more ways for people to level up spells, or temporarily get the 4th spell slot so many people desperately want.
The NPC (maybe Fortuna?):
It spawns with 3 randomly selected elemental specialties.
The magic teacher NPC works similarly to the trader and can be summoned using the wishing well or found in the map.
When interacted with (for a price in souls), it presents its 3 elements for the player to choose from. When the player selects one of these elements, they are given a random spell of that element in a 4th spell slot, and they gain spell EXP for that element.
Optional Part (Interesting but ambitious):
In this version, the soul cost is removed.
Instead of teaching with a price, the teacher in this version gives the player a curse of that element. Here's an example using the Pyro element:
- Player selects "Pyro".
- Player gains Surcharge in a 4th spell slot.
- Player gains significant spell exp.
- For the rest of the mission, player is damaged by water. Or player automatically sets off nearby explosives. Or player is occasionally targeted by a hostile fire beam.