@d6 It truly saddens me how many wizards nowadays have simply accepted needing to perform a ritualistic sacrifice _every_ lunar cycle just to keep their imp happy and there to help them work on spells.
Nearly any common woodland creature can be trained to become a Lesser Spellcasting Partner (LSP) that will serve as a wizard's faithful companion, that not only don't demand any sacrifices beyond needing to be fed and cared for the same as any other familiar, but are also _far_ more thorough than any demonic imp when it comes to helping to write and proofread newly designed spells. Plus they do so much more quickly! But they don't do nearly as much of the work _for_ you so Imps Are The Future!
Worse, some wizards have started turning to lesser imps that don't require a continuous connection to the underworld or regular sacrifices, but they still require _far_ more mana than other familiars, _and_ they're worse at their jobs!