K4350, Spellcaster

Whenever K4350, Spellcaster attacks, if it
has double strike, it gets +X/+0, where X is
the greatest toughness among creatures you control until the end of turn and can't be blocked this turn. If a player took combat damage this turn, that player exiles the top card of their library. Until the end of turn,
you may cast that spell without paying its
mana cost.