Demon Planets

Demon Planets are enemy planets in Planetballs, who first appeared in S2 Part 25: The Huge Disaster. They are known for terrorizing solar systems and being extremely powerful as they are immune to Ultra Killers® (as shown when Greeney tried to kill 3 with his Ultra Killer®) and utilizing powerful weapons.

False Demons
False Demons are demons who first appeared in Alternative Universes who are allies with the planets. They look the exact same as regular demons, though the only difference is they know compassion between the regular demon's enemies.

True Demons
True Demons are darker in color and originate from a dark force killing a false demon, in this form, they are completely immune to everything and need a real powerful blast to kill them (The United Family was able to upgrade Greeney Jr’s laser to kill them.

Trivia

 * It’s possible that the False Demons aren’t False Demons and rather Regular Demons that decided to ally with the planets due to how heartless and powerful the dark forces are becoming.
 * Due to the heartless nature of the True Demons, this might be the reason how the True Demons were named. And the interconnected episode (S3 E22, S2 E48 and S1 E34) show the demons have compassion so the True Demons being heartless compared to those demons make sense.