While the chances of this happening feel low, this did technically happen with the Goblin Storm precon and Goblin Lackey
So, although you might control a Bear Umbra and benefit from the land untap you cant move it to your own creature to try and trigger it (and the owner will probably not attack if you gain control of it, lets be honest)
If your cancellation is approved a 20% restocking fee will be charged
For example, the "commander tax," the additional cost to cast a commander from the command zone, is tracked for each commander separately
He makes a 1/1 Warrior when he attacks, which gets sacrificed on the next end step
Lead designer Mark Rosewater rated it 9/10 on his influential Storm Scale, indicating a mechanic which would require a minor miracle to ever be used in a new Standard set