Are there any lore reasons why an Archfey or a Celestial patron would give a character a fiendish familiar, or vice versa?

Question

My game group is pretty RP heavy and I'm playing a Warlock for this campaign. I'm in the first stages of character creation, and I know I want to do Pact of the Chain. I like the Imp as a familiar for a lot of reasons (shapechange, invisibility, Stinger, cool factor etc.), but I'm running into the issue of why some patrons would give me one. Fiends are obvious, and a Great Old one would totally corrupt an imp for my service but I was leaning toward Archfey or Celestial for the game.

Are there any lore reasons why an Archfey or a Celestial patron would give a character a technically fiendish familiar, or the other way (i.e. fiend patron with sprite familiar)?

Answer 1

It's not actually an imp

The Find Familiar spell doesn't summon an actual factual cat, bat, imp, pseudodragon, or whatever. When you cast the spell, what you get is:

You gain the service of a familiar, a spirit that takes an animal form you choose

And for the Pact of the Chain warlock, the spell is modified as so:

When you cast the spell, you can choose one of the normal forms for your familiar or one of the following special forms: ...

Nowhere does it say that it changes the fundamental nature of the spell - you don't get an actual imp, you still get a spirit that happens to be taking the form of an imp. The familiar's form reflecting your patron's nature is a stylistic choice that you aren't actually beholden to. The new options don't even override the choice of type that you get from the basic spell, so as written you could easily have a familiar that is in the form of an imp but is actually a fey or celestial spirit.

If you want your familiar to have the imp form for its mechanical benefits, but you don't want it to look quite like an actual imp, it'd seem reasonable to talk to your DM and ask if you can reskin the imp as some sort of tiny celestial servant rather than a little devil, if you want it to reflect a more heavenly patron. If I were your DM, I'd be happy to work with you on the flavour of the class/character in this way - it has no mechanical/balancing impact problems.

Answer 2

I put a similar question up on DnD Beyond, and I got an answer back I thought you all might find interesting. 'InquisitiveCoder' first covers the same mechanical information as Carcer then gives some gives some pretty interesting RP Ideas.

... A celestial spirit is still a celestial even if you give it an imp's form.

Since you don't need a reason to pick one familiar over the other, instead of struggling to come up with reasons that don't need to exist try exploring the consequences of your mismatched choices instead. Maybe your celestial or fey spirit isn't happy to be in an imp's form, but it's obligated to serve you. That's a great roleplaying opportunity. Is it resentful? Does it put up with it because it cares about you? Do you let it change forms every now and then - at your own expense - to make it happy? Their reactions to being in imp form can even be different by type. A celestial may despise being in imp form because fiends are evil, while a fey spirit might hate it because it's ugly, while a different fey spirit might think it suits their mischievous nature or like that you've given them what it perceives as the strongest form.