The Mooplexians are an alien race in Wander Over Yonder show.
They're weird-looking aliens who were the reason why Lord Hater became evil in the first place, since they were the first victims of Hater's pranks. However, their physical forms are only shells of their true selves, who live on in their minds.
In their physical forms, the Mooplexians have an odd grey-ish body with a single leg and foot, with magenta hair and two elongated eyes with pink pupils and a pair of feet on top of their head.
In their mental forms, they are highly advanced and intelligent, and looks more alien than before.
Cluckon, Cluckons's planet, had been invaded by Lord Hater and his Watchdogs, but the invasion eventually had failed because Hater suffered a funk. However, Peepers ordered the Cluckons to stay still because they was still halfway conquered. This caused them to exchange confused looks as the spaceship leaves.
Peepers and the watchdogs did many things to cheer Hater up (blowing up a moon, terrorizing people, awaking demons, etc) but all their attempts failed. Later, Lord Hater told Peepers that when he first started wanting to be evil when he used to just pick on the "weak and defenseless", but was now tired of his new responsibilities and others things. Peepers soon thought of an idea that would likely get Hater to be evil again.
He fixed up Hater's old van and brought him at night to Mooplexians. Hater and Peepers then did many immature pranks on them (spitballs, water bucket trick, loogies, etc). In the morning, Lord Hater felt evil again.
But then, the Mooplexians flied up to the skies and their leader used their stems to connect it to Lord Haters and Commander Peepers heads. Using telepathic torture, he explained that they actually had high intelligence, possessed endless knowledge, and spent their real lives in their minds. They flicked Hater and Peepers into the van and went back into their brainless states. Wander and Sylvia arrived on their planet, since Wander sought their wisdom, but Sylvia was in disbelief in how stupid they seemed.