So you want lore of the other shapes eh?
Aight.
HeartStreaker (or Crush because that’s his nickname) is basically supposed to be a shape version of Cupid, but the two Axolotls decided to make him an alchemist.
Leafy is actually the dragon guardian of some ancient forest created by Orbit, but was given the ability to shapeshift into things like a pentagon.
Cryo is born a shape demon to assist the Axolotl twins of Time and Space (like Octa and Hex), she was born when Orbit mixed some of Octa’s DNA with some ice, which is why she’s his sister.
Mucky was born from a radioactive meteor.
Nekogon was a normal yokai but he got fused with a hexagon.
Octadog was a normal beagle, but she got hit by a car and got her soul fused with an Octagon.
And Goldentooth died from drowning after a sea monster attacked the ship he was on, but the Axolotl twins fused his soul with a pentagon.
Surprisingly enough, there were also a whole population of shapeshifting shape demons that were fused with the souls of people who died, there is even a realm where they are a bunch of them, the realm is kinda like a spirit world for human (or other kinds of) souls, some of them even got the same kind of powers as the main 4 shapes, like the 4 “counter” shapes.
Halogon used to be a guardian of the Afterlife, but AngelBunny had to remove him from Heaven due to him being extremely annoying (reason? he was always making a whole bunch of bird noises, thus interrupting the other angels’ peace), so instead Orbit allowed Halo to guard the shape world.
Unfortunately, only the Axolotl twins or an alchemist that assists them can give the shape souls powers, otherwise the only powers they’ll have are shapeshifting. Usually they’ll just keep the shape demons that way so they can live “normal” lives as ghosts, but will sometimes give powers to the ones that seem “special”.. well, to Nebula at least.. but Orbit made a BIG mistake of giving Cobalt and the 3 other “clone” shapes some powers, since now they are using it to try and kill the 4 main shapes, so Orbit punished them and sent them to something called the “Glitch Dimension” (which was made by the Glitch Dragon, aka Yuánjiàn), where there’s another ball of slime named Sludger, who got trapped there after he tried to kill Mucky.
So there you go.