gremlin help, please

[Robbert Raets]

Suppose I were to add one level of sorcerer to a quasit or imp, and then give it a reduced version of the (item) possession ability from the book of vile darkness. What CR would it have? 3? 4?

...Suppose I would populate a steampunk world with them? Would that increase the CR?

 

[Krishnath]

I say, up their original CR by 1.