Shelled Kraken Dragon

When this creature enters the battlefield If X
was more than 7, kill that many creatures your
opponent controls.
{1}{b}{u}: Destroy target artifact
or creature with mana cost 3 or less
Hexproof, Sinker:(When this creature attacks,
target non-flying creature gets a -1-1 counter
and can't attack or block until that players next turn)
This creatures toughness is equal to X.