Flint, Stone Enthusiast

{x}{w}{g}- Create {x} 0/2 Wall Artifact Creature
tokens with Defender and the ability "Sacrifice
this creature, do {x} damage, where {x} = it's
power, to any target. If the target is a creature or planeswalker, do excess damage to the target's controller"
At the beginning of your upkeep, add a +1/+1
counter to all walls you control