When Tararat used his mana, he had a tendency to become more hot-blooded. He didn't think as much as when he kept a lid on his mana. Or rather, he didn't need to think as much since his overwhelming power would be enough to settle any problem.
Even problems without physical solutions could be solved with Tararat's rationale.
He didn't necessarily need to bring Ackster back to the elders alive so they could fish out the truth from him. He just needed to bring his corpse, at most, and tell them what Ackster had told him. If they could discern the truth from that, it still wasn't a big deal.
If Kargas really showed up with something from the Alchemaze powerful enough to destroy the Land of Dragons, they just needed to prove him wrong with overwhelming force.
So, Tararat stopped holding back entirely as he cut down with his sword, aiming to cut Ackster in half.
