Questions about familiars

[FrozenGnomes]

I will be taking improved familiar on my fiend-blooded sorcerer, because I want a cool familiar. A couple of questions though. What exactly CAN be a familiar, in terms of what are the criteria it needs to meet? I've seen plenty of lists, but I dont know what metric they're going off of.

Second, sort of in line with the first question. How do you go about brewing one up? There's a non-zero chance that I could convince the DM to let me take a homebrewed one. What's the process for making a familiar out of a random beasty?

[Kayblis]

Almost any creature can be a familiar. The only restrictions are that it must be roughly the same size and power of a common/improved familiar(so around the same CR and size category). To create a new one, simply pick a common creature that mets the above general criteria and have it be of a close alignment to yours(Celestial/Fiendish is the easy route, if it's an animal; doing it by subtype is great too). Then apply the Familiar modifiers. The rules are very broad to allow for whatever the player wants and doesn't break the game with DM approval.

[FrozenGnomes]

Ah, lovely. Fiend-blooded applies the fiend template, or whatever its called, to your familiar. Any particular suggestions? I have almost no knowledge of the extended 3.5 bestiary. Am 8th level caster if that helps.

[Efrate]

imp and quasit are very good

[MaxiDuRaritry]

You could always take the changeling wizard racial substitution level. Your familiar can turn into any creature you can take as a familiar as a [Su] ability. It's from Races of Eberron. You don't have to make up your mind for what kind of (improved) familiar you want, unless it's which one you want right now. Of course, if you take levels in spell sovereign (Dragon Magazine #357), you can turn your familiar into a living spell, which is an ooze that can cast the spell it's made from at will. That means you can have access to literally any lower level spell in the game, as often as you want it. The Obtain Familiar feat just makes this even more borked.

[Elkad]

Any improved familiar with hands and a voice (to activate items) is a powerhouse.

Throw in things like unlimited invisibility and fast healing and it gets even better.

Imp is a personal favorite, but really nearly any outsider or dragon will do.

And have a handbook
http://dictummortuum.blogspot.com/2011/08/familiars-handbook.html

[Malphegor]

Personally, I'm fond of the Imp, mainly because it can consult dark gods if you're stuck with a puzzle (Ask the DM the answer! He won't screw you over at all!), and also because it can transform into fairly standard normally familiars, so if you're in a society where people don't look kindly on someone carrying around a demon baby, you can be 'zim zalla zim, there is no infernal being here, merely a slightly tempermental bat!'