The Auto-Siege

The Auto-Siege's power is equal to the number
of walls in all graveyards, and can't be blocked by
walls.
Walls you control have "{t}: add {c}. Spend this
mana only to cast Juggernaut spells."
Juggernauts you control have "Whenever this creature attacks you may sacrifice a wall. If you
do deal damage equal to its toughness to target
player.