Mirrored Slifer the Sky Dragon

Flying
Cannot be countered
When Slifer enters the battlefield, spells cannot be cast and abilities cannot be activated.
When Slifer enters the battlefield, put a +1/+1 counter on it equal to the number of cards in your hand.
Slifer's power and toughness is equal to the number of cards in your hand.
{t}: Destroy any creatures with 4 or less power.