Robert Baratheon, The Usurper

Dethrone, Trample
Whenever Robert Baratheon, The Usurper
attack, you may destroy target legendary
creature. If you do, create a 0/1 black and while
Lannister Noble with "This creature can't be
sacrificed" and "This creature can't block"
At the beginning of the end step, if you control
four or more Lannisters, you lose the game.