Breath of Fury attached to a creature without summoning sickness ).
Notable Prerequisites
You control a nontoken creature that has haste and that does not have
Breath of Fury attached to it.
An opponent cannot block creatures you control.
Steps
Deal combat damage to an opponent using the nontoken creature that has haste and the creature that has
Breath of Fury attached.
Breath of Fury and
Impostor Syndrome trigger.
Resolve the
Impostor Syndrome trigger, creating a token copy of the nontoken creature with haste that isn't legendary.
Resolve the
Breath of Fury trigger, sacrificing the creature it is attached to and attaching it to the creature token created in step 3, then untapping all creatures you control and causing you to get an additional combat phase after this one.