Favourite magical pet?
Ah! Too many to name. But I will try)) So... if I were looking for a magical pet, I would seriously consider an Owl, a Phoenix, a Crup, a Puffskein or a Pygmy Puff. But the first that always comes to mind when I think about magical pets and that always makes me go squee is definitely a Niffler. Unfortunately, it would be totally disastrous to keep one as an actual pet unless I lived in a cave or under the ground. We first encountered these creatures in GoF during Hagrid's Care of Magical Creatures lesson and I immediately fell in love with them, because they are totally cute and useful too (if you're looking for treasure)! Here's their description from Fantastic Beasts & Where to Find Them by Newt Scamander:
NIFFLER
The Niffler is a British beast. Fluffy, black and long-snouted, this burrowing creature has a predilection for anything glittery. Nifflers are often kept by goblins to burrow deep into the earth for treasure. Though the Niffler is gentle and even affectionate, it can be destructive to belongings and should never be kept in a house. Nifflers live in lairs up to twenty feet below the surface and produce six to eight young in a litter. (The picture is take from The Harry Potter Lexicon)
Just look at it! What a cutie))