What are the rules for picking something from Improved Familiar in Pathfinder? How do you know what familiars are available — is it only the ones listed on d20pfsrd.com or are there rules that let you pick your own familiar from any monster in the book?
The only rules they list on d20pfsrd is that it has to be compatible alignment and have to be a sufficient level but that's it. I thought there was one more saying your familiar can't be as tall or taller then your character, so if you're medium your familiar has to be small or smaller. But I can't find that final size restriction rule anywhere.