Skyrim basically has that first one if you count becoming a Werewolf, though it's only really a boost in strength and the like if you started out weak with not great armor.

Granted, if you're a wizard, that probably should be a boost in strength and the like. It's just that being a werewolf is just a thing anyone who plays can do, so it's not really a cool thing a school of magic can do. It's just a thing you can do if you do the right quests.

I've never played a game that lets you be sneaky via shrinking, and I definitely think it should be a thing. I know there'd be some problems with it (such as suddenly seeing textures much closer up), but I'm sure it could be done well.