My line of thinking was that wolves help you with combat, so cats would help you with magic.
If new domestic animals are added, like birds or what have you, I wouldn't be terribly opposed to having one of them as a familiar. But I think wolves already have their niche, even if they could stand an AI upgrade.
This seams a great idea, I think familiars should be able to "talk" to you. Like voice acting or using the chat to say things. Talking could be implemented for it to say it's "health is low"(self explanatory), "run away for your lives!" (when health is low and it's under attack)," bow before me creeper" (when a creeper flees from it), "your doing wrong give me that" (when your brewing or enchanting), and other things under those lines. Maybe if familiars are exposed to certain types of magical substance to could slightly transform, like go fiery when going around nether rack or become and ender cat when you use enderpearls often.Another use for familiars would be in Thaumcraft where a familiar could be an owl or a raven (an animal that is considered wise) that guides you along the path to great magic, and it could tell you not to cover the world in taint.
An idea for spells would be unnatural growth like trees with doors and vines as ladders inside and mushrooms with almost ready tnt cannons.
. I keep on thinking iron should repel it, what with what you mentioned about it possibly being a fae creature within the familiar, although I'm not sure if that's actual folklore about fae or if it's something I've gotten from Terry Pratchett's Discworld series or both.
Pratchett took the thing about iron from folklore.
If new domestic animals are added, like birds or what have you, I wouldn't be terribly opposed to having one of them as a familiar. But I think wolves already have their niche, even if they could stand an AI upgrade.
An idea for spells would be unnatural growth like trees with doors and vines as ladders inside and mushrooms with almost ready tnt cannons.
Pratchett took the thing about iron from folklore.