Realistically? I don't think Meta Knight would ever have a pet. Reason being he wouldn't have the time to dedicate himself to one, and I feel that he's the kind of person who believes nobody should own anyone else. However, if he had to have a pet... I could see him raising a pet Scarfy! If it had to be a real world pet, then probably a cat. Something independent that comes and goes would suit Meta Knight the best.