Plus, Goats
The design for this was based on Mistform Ultimuss ability, and it was later featured on creatures from the Lorwyn block like Shapesharer
Theres a reason why this effect is colloquially named after this card
Play Rule #13 states: Abilities which refer to other cards owned outside the game (Wishes, Spawnsire, Research, Ring of Ma'ruf) do not function in Commander without prior agreement on their scope from the playgroup. Therefore, Spike is twice banned in Commander, and even if Unstable were allowed, Spike wouldnt be able to be played
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Threaten, on the other hand, only works until the end of the turn, so you have to return the creature to its legitimate owner after that