Allies were first introduced in Zendikar, reused in Worldwake and returned in the Battle for Zendikar block
At the beginning of the chosen players upkeep, this artifact deals X damage to that player, where X is the number of cards in their hand minus 4
Its ability to grant each player an additional card can be a double-edged sword, so it works best in decks that can capitalize on the extra cards while mitigating opponents' advantages, perhaps through counterspells or other forms of disruption
Wide shelves can hold more stock than a standard shelf
An ability this strong makes Teferi a magnet for removal, but if he manages to hit the battlefield, he'll likely win you the game, assuming you're using him to combo off without being interrupted by a counterspell
It's one of the best X spells to dump your mana into