Fierce Havoc

Cast only if a creature you control dealt lethal
damage to a permanent during combat this turn.
Untap all creatures that attacked this turn. They
gain fierceness 2 until end of turn. After this
main phase, there is an additional combat phase followed by an additional main phase.
Flashback—{2}{r}{r}{g}{g}, Remove four +1/+1 counters from any number of permanents you
control