So I’m just recently made a concept for a character, a red Dragonborn bladesinger / fighter.  (Yes I know he isn’t an elf).  One of the spells I plan on taking is fine familiar, but I’m not sure which form to use.  I will mostly use fire-based spells, so I wanted a familiar to match that theme. Help please?

A (fire)fox? ;)

I’ll ask my DM if he’ll allow that.  I sure he’d get a kick out of it

Pseudo dragon 

Try for a giant fire beetle.

The spell says you determine if your familiar is celestial, Fey, or fiend. Consider asking your GM if it can be Elemental instead. The difference is bound to be insignificant, unless you want your familiar to be able to do specific fiery things. 

Using the raven or owl as a template you could say it is a phoenix. Abyssal chicken was added in for BALDUR'S GATE: DESCENT INTO AVERNUS. 

Quote from halfling2099 >>

Using the raven or owl as a template you could say it is a phoenix.

This is precisely what I did with my Fire Genasi Wizard. Stat wise it's just an Elemental Owl - but it's a baby phoenix.

Quote from OboeLauren >>

Quote from halfling2099 >>

Using the raven or owl as a template you could say it is a phoenix. Abyssal chicken was added in for BALDUR'S GATE: DESCENT INTO AVERNUS. 

 Abyssal chicken is pretty spot on, IMHO. Also they're just awesome. And if you get tired of them they turn into amazing buffalo wings!

As long as your DM is ok with flavor that don't affect mechanics, you could go for a fire newt or some other fire lizard. 

 Is there any reason a familiar being able to set unattended objects on fire would warrant a CR adjustment or otherwise break the intent of the spell?