I am toying with a concept whereby an aberrant sorcerer gets his power essentially by being part of a cranium rat swarm. Whether he is a central mind that dominates and draws power from them, is a hapless puppet that is a convenient face for them, or is literally just another body in the hive mind is a question with, conceptually, a deliberately vague answer, at least at this stage (as I could see it going any direction, depending on the game and other factors).

What I am debating right now is whether to simply use a refluffed Mark of Handling Human, or adapt the Yuan-ti Pureblood by changing the target of its unlimited-use animal friendship from snakes to rats

Either way animal friendship can charm a swarm of rats that can be fluffed as his cranium rat swarm.

Any suggestions on which approach to take, or alternative ones, or on how to better get a convincing "cranium rat swarm" ally/companion are welcome.

Thanks!