|2 people marked this as a favorite.|
If this is because the player wants to change classes, just let them do it via the Retraining rules in Ultimate campaign, rationalized by their increasing affinity for _____ over time, and possibly including some big epiphany moment like described.
If this is because something about the character is unbalanced, take the player aside and talk to them about it. Let them make changes for free and work with them to rationalize in-game what happened.
If this is because you feel it would make an interesting story, just don't. People don't like when you force them to do things they didn't want to do. They wouldn't have made a druid if they didn't want to be one. If you force things like losing powers and class changes on your players, you'll quickly find that nobody wants to play with you as their GM. Most seasoned players have at least one horror story of a GM who was too heavy-handed, and you don't want to be remembered as "Jim, that GM who made lose my druid powers for no f***ing reason."