Breath of Fury attached to a creature that can attack this turn.
Hanweir Garrison does not have summoning sickness.
An opponent is unable to block and kill creatures you control.
Steps
Declare Hanweir Garrison and the creature with Breath of Fury attached as attackers.
Hanweir Garrison triggers, creating two 1/1 Human creature tokens that are tapped and attacking.
Deal combat damage with Hanweir Garrison, the Human tokens and the creature with Breath of Fury attached.
Breath of Fury triggers, causing you to sacrifice the creature it is attached to, attach Breath of Fury to a Human token, untap all creatures you control and get an additional combat phase after this one.