1 Urza, Lord Protector + The Mightstone And Weakstone = Urza, Planeswalker The hero of The Brothers War, Urza combines with the two stones that sparked the conflict with his brother, The Mightstone and Weakstone, to become the legendary Urza, Planeswalker
I think we can officially call it
What makes them the best way to protect and organize your growing collection
Instead of containing just weak cards to provide a baseline, it seems this set will have quite a few powerful inclusions - though nothing that's likely to attract a ban
you may exile target non-Horse creature you control that wasn't put onto the battlefield with this ability this turn, then return it to the battlefield under its owner's control
Magic R&D always sets out to make new set mechanics that are interesting to play and (usually) playable in the competitive sphere