Dimentio, as mentioned above takes the appearance of a jester, and He suffers from a Jekyll-Hyde persona. Probably explains the black-white color on his mask, which resembles Yin and Yang. He was so evil that he has fun brainwashing victims (i.e. Gamzee Makara and Eridan Ampora just to make them evil AGAIN), and he laughs hysterically while doing so!
Dimentio is able to torture, torment, brainwash, or send his victims to another dimension with his right hand without any special kind of equipment, but rather magic.
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He is easily comparable to the mad titan known as Thanos in that they are both powerful beings who snap fingers and are purple. The only difference is that Dimentio snaps with his right hand to torment his victims while the latter snaps with his left hand (With the Infinity Gauntlet) to turn half of the UnUniverse into dust. Dimentio is also weaker than Thanos.
Dimentio once caught Silhouette and sent him to the Dimension Jail, but the latter escaped from the former's prison.
He fused with Luigi after brainwashing him back into Mr. L to become Super Dimentio, though he got his @$$ kicked by Ronald McDonald and his team.