Seeing Tony in position, Trinal darts forward and positions himself behind A and B. He'll attempt to be stealthy and avoid giving away his movement to the Chulassa.
Stealth: 17+6=23
Unleashing Tempest Breath, he'll catch both A and B and their mounts in the effect.
Attack: d20+13 vs reflex, damage 2d6+10 (if any surprise applies, feel free to adjust)
Attack: 20 (crit) + 13=33
Damage 5+10=15 (is a nat 20 automatic max? if so, it's 22)
Crit roll: 100%
(I took a photo of the dice, which may not mean much, but I really did roll them)
Photo evidence:
A man may fight for many things. His country, his friends, his principles, the glistening tear on the cheek of a golden child. But personally, I'd mud-wrestle my own mother for a ton of cash, an amusing clock and a sack of French porn. - Edmund Blackadder