Viserion, Keen Eyed Warrior

Flying, Mentor, Vigilance
Militia- If you have 4 or more creatures currently
on the battlefield, Viserion, Keen Eyed Warrior becomes unblockable until
end of turn.
Keen- If target opponent has only 1 creature on
the battlefield, as long as Viserion, Keen Eyed
Warrior attacks that opponent he has double
strike until end of turn.