Every once in a while Blizzard designs some incredibly strong cards, and Carnivorous Cube is one such example. This 5-mana minion has one of the most OP effects ever.
Surely, first you need to remove your own minion from the board, which may give an advantage to your opponent. But that's only before the Cube dies, as later it will bring back twice as many threats to your side.
It could also be well paired with a Spiritsinger Umbra that will trigger the deathrattle effect after the battlecry, making your board look super intimidating.