Quote Originally Posted by Rixx View Post
You use the creature's Challenge Rating (CR) as its total "monster levels" - and take the rest as Sorcerer levels.

Imps are CR 2, so you'd be Imp 2 / Sorcerer 4.

Halfway between party levels 8 and 9, take an extra level in Sorcerer, to compensate for your monster levels becoming less useful.

For the record, your ability score adjustments would be +6 Dex, +2 Int, +2 Wis, +4 Cha.
Sure it's this simple?

The guy who explained it to me made it sound like I would get one level for the cost of three regular levels, and that would go on for (CR/2)x3 levels. Or the like.