Desert
See, this is why the triplets made sure to get far, far away from the ice-encrusted rocks. By whatever bizarre laws of physics this dragon operates upon, those things were ticking timebombs.
Well clear of the blast radius, the triplets continue to fire! Or at least Alpha and First do, One isn't quite content to just keep taking cheap shots at the dragon from a distance. No, a warrior like this 'Diinuldrum' deserves to be finished off in style.
Drawing his sickle One slashes into his left arm with it, his own blood feeding the weapon's magical properties and increasing his speed as he turns to run directly at the dragon.
Assuming he manages to get there without being frozen solid or forced to turn back in order to avoid the dragon's icy breath, he'll try to dash right over the creature's back and sink his blade into the base of Diinuldrum's neck.
No doubt the dragon's armor is rather thick there, but with his boosted speed also increasing the strength of One's attacks he should be able to pull it off. Force equals mass times acceleration and he's got plenty of that last one.