Quote Originally Posted by Altair Vex
I've not seen the original Diabolist, but this seems nearly balanced to me...

Only nerfing thing I'd suggest is changing the Diabolism damage. Maybe less increases (so it only gets up to 3d6), lower die type (d4 in place of d6), or less times per day (once per day per two Diabolist levels, but at least once).

You might want to note that the Imp familiar eating the previous familiar has all the associated penalties of losing a familiar.
Oh, I forgot to type in the part where it says the previous familiar's abysmal end has no effect on the original caster.

and I think I agree with you on a change to do with the times per day diabolism