Besiege the Command Tower

At the beginning of each opponent's upkeep,
if their commander is in their command zone,
Besiege the Command Tower deals 6 damage
to them.
{x}, {t}: Target commander you control gets
+X/+0 until end of turn. It fights target
opponent's commander. (If that opponent has
multiple commanders, they choose one.)
"Combo piece?! Just for the colors?! Get out and fight!"