Mildwin resembles all the other Moldos. He is a slug-like blob with a round mouth and large eyes, though he is slightly larger than the others. He has a purple mouth, green eyes, and yellow-brown skin. He wears a brown bottle cap on his head as a crown.
As with all the Moldos, Mildwin is capable of climbing up sheer surfaces and using his mouth to cling onto them, making him difficult to remove. They also seem to be capable of building primitive weapons such as spears, and crafting cages from rulers.
Despite being the antagonist of the episode, Mildwin has shown to be a pragmatist and not evil. He holds no ill will toward the Pagelings for their past battling and only wants what is best for his people.