Both have a great board presence as solid trampling bodies that can swing and win, while also having shroud/hexproof to keep your foes from mucking about and slaying it
If it's legendary, it also gains trample until end of turn
Sure, copying the right legendary creature just twice might be enough to win you the game, especially if were copying Kozilek But think of the possibilities
Regardless, the rare MTG card has managed to outdo its own legendary reputation by selling for over half a million dollars not once, but twice - before having its record broken for a third time mere days later
I love that it encourages attacking and will be particularly awesome at boosting a small flyer that an opponent will have a tough time blocking
It often goes further with draw-sevens and infinite combos that involve Crucible of Worlds to make this a 1-mana game-winning play