dcollins
Explorer
I use the DMG Ch. 2 "Variant: Gaining Class Abilities", somewhat softened, requiring a 1/2 week per level of training in a town at a cost of 100 gp/week. This provides the rationale that everyone needs to train/study to pick up their new skills, feats, attacks, abilities, and spells. Admittedly, this is a variant that I've gotten quite a bit of resistance from some of my players.