Breath of Fury and Leonin Warleader on the battlefield.
Breath of Fury attached to any other creature you control.
An opponent cannot block creatures you control.
You control at least one Mountain.
Steps
Declare Leonin Warleader and the creature with Breath of Fury attached as attackers.
Leonin Warleader triggers, creating two 1/1 Cat 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 Cat token, then causing you to untap all creatures you control and to get an additional combat phase after this one.