You know what I want to post this even though I know it's wrong.
It sounds to me like it 's Poo from Earthbound.
1: When you first get poo in earthbound you must let your master "kill" you. Then he gets sent to Ness and Co.
2: Technically he's not in ssbm, but he is a trophy
3:His only weapon in the whole game that doesn't make him lose attack points is the Sword of Kings. Ness, Jeff, and Paula use exactly 40 weapons including slingshots and yo-yo's
4: Can you say Mirror attack, in Earthbound Poo can mirror an enemy and he can then use all there attacks. One of my more favorite things of Earthbound.
I doubt that any of this is correct, but if it is, Yay me, because then I'm alowed to do clues again