Combat Celebrant

If Combat Celebrant hasn't been exerted this
turn, you may exert it as it attacks. When you
do, untap all other creatures you control and
after this phase, there is an additional combat
phase. (An exerted creature won't untap during your
next untap step.)

"We've had too much bloodshed. I think a cleansing
is in order. So, consider this an invitation from my
family... To yours."
—Cesare Borgia