While Sans has also lost track of the objective here, at least part of it is driven by magical compulsion and therefore not subject to debate. One thing must occur without question: the Nightrider must be defeated. He was meant to collect those that defied the Prince and bring them to him.

The poison has been working, but not quickly enough, and Sans's anger is getting in the way of carrying out his mission smoothly. The human's audacity is enough to fill him with fury, leaving him desperate to win out of some need for purpose. He helped to teach Lambert these techniques. How could he be so pathetic as to lose now?

Despite how durable he is in this form, he's been knocked around enough that his joints are beginning to rattle and shake. He's exhausting himself with his own excessive use of firepower. Still, his animal impulses have begun to crave only one thing - to destroy this enemy and to take that strength into himself, just as humans always feared they would. Give them something to actually be afraid of.

Lambert is just about to lock those fangs around his spine when he teleports away one last time, out of the dragon's grapple and into the air above him, slamming down onto his back and digging in that tail barb one last time. Fire and light builds in his jaw, ready to roast the dragon beneath him-

It's only then that Sans stops, because he can sense someone of importance nearby. Not Peridot, with her frantic attempts at distraction, but his own master, coming to collect his prey.

He holds that fire in his throat, ready to let loose - but he doesn't. Not without the Prince's permission.