An opponent is unable to block and kill creatures you control.
Steps
Declare Giant Adephage as an attacker.
Deal combat damage with Giant Adephage.
Giant Adephage and Breath of Fury trigger.
Resolve the Giant Adephage trigger, creating a token copy of Giant Adephage.
Resolve the Breath of Fury trigger, causing you to sacrifice Giant Adephage, attach Breath of Fury to a token copy of Giant Adephage, untap all creatures you control and get an additional combat phase after this one.