90% of the creatures printed in the new expansions are all overpowered. To fix this you need to ban all creatures that have

Lots of abilities without any sort of meaningful drawback.
Power and toughness that exceeds its mana cost.
Abilities that can give more than one +1/+1 in any turn.
Whose power and toughness can increase in response to a trigger.
That have abilities change rules of play like Voice of Victory and Bloodletter of Aclazotz