Also, standard procedure is to write out that this has vigilance separately

Wow. That's one seriously efficient bear.

I would reword as "Whenever enchanted creature becomes the target of a spell or ability, counter that spell or ability unless its controller pays " to avoid confusion about abilities that don't have costs like most triggered abilities.

I wanted a concept of horcruxes but I wasn't quite sure the best way to implement them.

Maybe you're thinking of Sectumsempra? :P

(I don't have anywhere near good enough memory, but I'm certain there'll be at least one wiki somewhere with all the details.)

Borrowing concept from Swift Keeper

I can't remember, I thought diffindo could cut flesh as well as cloth, but now I look it up I'm not sure if it can. Anyone sure?

I don't like that Lily's only real ability is to sacrifice herself, but that's what's in the books. At least I made her a bear.

I'm not positive about the protection ability. It's a middle ground between "gain control of target spell" and "change the targets of target spell". What's a good cost? That's usually blue, but red felt more appropriate flavour wise, and red gets change target as much as blue.

Originally it was just "hexproof", but the "redirect spell" flavour was obviously necessary once I thought of it...

What else was James famous for, other than flying, being an animagus, being a jerk and being brave?

The combination of flying and animagus is quite potent. That's probably good, but I don't know about the costs.

I'm not sure about the mana cost. James seems red, but a small flying creature is more W and James could be W.

The same applies to Harry, I think he's more R, but he could also be W.

"hexproof + unblockable" is a good combination for "invisible", but a really annoying one to play against. So here we have unblockable + partial hexproof, which is hopefully still well worth having, but not as overpowering.

And fits the cloak quite well -- it's harder to aim a spell at someone in a cloak, not impossible.