A player wants a magic item to fully change their class on the fly and I don’t know how to feel about it.

So I understand how the title should immediately pull a ‘fuck no’ from most of you but I feel like this is really the fault of myself and not planning better pre-campaign/ at session 0.

For context we’re running a Pokemon DnD campaign where the players are the Pokemon, kind of in a Mystery Dungeon style. The parties currently level 9 and one of my players who I’ll refer to as W is a Sableye Rogue who at the end of last weeks session (We run bi-weekly for context) rolled insanely good skill checks and managed to steal a Sablenite (Megastone) from a museum.

Me and W were discussing the potential homebrew features and what the Megastone could do for his character this weekend. My intent was to have the larger gem act as a form of cover for W, and also as the dex entries for Mega Sableye describe the ability to reflect some spells/aoe damage. Admittedly in retrospect this does seem kinda lame, especially with it basically locking W’s Rogue to a singular location, and W communicated how he felt a bit unsatisfied with that.

The solution he proposed was that, as the gem would cripple his movement, that it could pivot his play style into a stationary sentry style of spell caster, using the gem as a focus and essentially trading in his levels in Rogue for a spell caster, ideally for him Shadow Sorcerer.

Frankly this does sound really fun in my mind and on my table we’re not at all rules lawyers and go by the rule of cool a decent lot but at the same time I’m finding it difficult to justify giving this to him, especially when I don’t think I could give similarly fun mechanics to the other players with some of them.

TLDR: My player wants a overtuned magic item which I’m somewhat fine with, but I’m struggling to justify giving it to him without neglecting the other party members.