As the dm what I would do is allow it, but let the player know:
“ultimately this is too powerful to allow long term, so the goal here is you are going to succumb to your instincts and eventually turn and our leave the party and become an npc”.
and then let the player role play it out. Hence this becomes a cool cinematic boon instead of a long term OP issue.
“ultimately this is too powerful to allow long term, so the goal here is you are going to succumb to your instincts and eventually turn and our leave the party and become an npc”.
and then let the player role play it out. Hence this becomes a cool cinematic boon instead of a long term OP issue.