Breath of Fury attached to any other creature you control that does not have summoning sickness.
An opponent cannot block creatures you control.
Steps
Declare Grave Titan and the creature with Breath of Fury attached as attackers.
Grave Titan triggers, creating two 2/2 Zombie creature tokens.
Deal combat damage using the creature that has Breath of Fury attached.
Breath of Fury triggers, causing you to sacrifice the creature it is attached to, then attach Breath of Fury to a Zombie token, then causing you to untap all creatures you control and to get an additional combat phase after this one.