Blue Dude

Before
A radical skier and also a radical eco-terrorist. Blue Dude took it too far after listening to I'm Blue by Eiffel 65. Ever since the dawn of time, Blue Dude has been fascinated and inspired by Thanos Dude and his actions. Blue Dude devoted his entire life to fulfilling the events that needed to happen in order for Thanos Dude's success. But eventually Blue Dude realizes that Slope Dude is the Math Defender of Earth.

Slope Dude 2
Blue Dude races Slope Dude in the attempts to beat him, but he sadly loses the race.

Slope Dude 3
Blue Dude take his revenge on Slope Dude by confronting him out of nowhere, ripping the ground beneath them. Blue Dude smashes Slope Dude into bedrock where he traps Slope Dude in an endless flood of water.

Slope Dude 4
Blue Dude then realizes due to his constant failure that he's starting to become irrelevant to the story line, so he decides to pump it up a notch. Blue Dude goes after Sans, but Slope Dude flies in and intervenes. But Slope Dude decides it's best to let them be, and Blue Dude and Sans continue to battle. As Slope Dude flies away in his new sick Ultra-Shiro Prime armor, Blue Dude gets the idea to build a suit for himself. Once Blue Dude and Sans fall and hit the ground Blue Dude realizes he must stop Slope Dude and then escapes the situation with Sans confused. Blue Dude then constructs his mathematically aerodynamic wing suit. By the time Blue Dude finds Slope Dude, Thanos Dude is almost defeated, so Blue Dude sweeps Slope Dude away dropping the Division Square which Thanos Dude longs for. Blue Dude flies Slope Dude to an abandoned slope as he tries to explain to him why Thanos Dude is right. Shortly after, Blue Dude leaves Slope Dude be as Slope Dude dusts away soon after.

Beyond
With Thanos Dude succeeding in his plan, and presumed dead, Blue Dude sees no other purpose and no longer exists for plot reasons.