Umori, the Collector in Workshops
Since most Workshop decks are all artifacts and lands you can play Umori, the Collector in your sideboard as your Companion. I know there isn't very many colored mana sources to cast it but it only takes up one side board slot and I think it would be OK to but in two Urborg, Tomb of Yawgmoth to help pay for it's cost. Also by adding Urborg in, your Ancient Tombs can produce mana without having to cost life and Mishra's Workshop can produce mana that can be used for other purposes than casting artifact spells, also good for Dismember.
Also hits Bolas' Citadel
Doesn't stop Oath of Druids, Dredge's free creatures, or Tinker. I think most actual spell-casting in Vintage does take place from the hand
Human Tribal creature that hates on snapcaster, Dredge stuff, Flashback, the new companions, and a few other things. Probably not enough on his own but could see sideboard play as supplemental hate that hits a few different archetypes.
Uhhh, Donate wouldn't do much there. You'd just be giving them a creature. You can call a judge if you like, they'll just stare at you.
Companion is something you declare at the beginning of a game, sort of like Commander. Once the card is cast and in play, it's treated like any other creature.
Yeah, I'm aware of that. I was just pointing out that the only reason why this would ever see play would be to try to troll someone that way.