Unstoppable Offensive

All creatures able to block this turn must do so.
At the end of combat, if a creature a defending
player controlled died or the defending player
has no creatures, untap all creatures you control.
There is an additional combat phase. Repeat this
process any number of times.
"Our grip tightens around the black heart of
Berlin. If they stand for Germany, they die for
Germany. Building by building. Room by room.
One rat at a time." -Viktor Reznov