I actually have a theory about Toffee, and his "unpleasant" history with the royal family.
During the Mewman-Monster War, the Monsters found themselves on the losing end of the fight. My evidence of this can be found in Mewnipendance Day, when Star decks out Marco and company in far more superior armor and weapons than what the monsters have. So, in an attempt to turn the tide of battle, the magic-versed monsters pooled their powers together to create a creature who would fight for them. A creature who could never be truly killed, who possessed the ability to heal his wounds as quickly as he suffered them, who was more devious, sly and cunning than anyone or anything could comprehend, who knew magic inside and out and could wield it at will, and finally, who would wage unending war against the Mewmans, overthrowing the royal family before culling every last living Mewman until there are none left. That creature's name was Toffee, and fit the bill he was given in every battle he fought in. Of course, the Mewmans won the war, and Toffee went into hiding, meticulously planning for the next great move against Mewmanity.
Cut to the present day, when Ludo is waging a struggle against the Mewnian royal family to steal the Royal Magic Wand. Disguising himself as a mercenary for hire, Toffee learns about Ludo's request for assistance in stealing the wand. Seeing his chance to get back at the Mewmans, Toffee accepts the offer, before slowly but surely taking over Ludo's assets, such as his army and castle. He planned to force Star into severing the wand crystal in half, knowing it would destroy his physical form but not his spirit, which then inhabited the severed other half of the crystal. Knowing Ludo would find it, he fused the crystal with the skeletal remains of his right wrist, forming an evil wand. He then spoke to Ludo telepathically, convincing the bird monster to bring Star to him. Ludo failed, but instead he took the Butterfly's spell book, which Toffee worked his plan around. He convinced Ludo to open the forbidden section of the book, telling him the false promise that the forbidden section would grant Ludo powers greater than anything he'd used so far. Instead, Toffee possessed Ludo and the rest is history. Now, with the crystal embedded in his palm, and with the powers of Queen Moon and the Magical High Commission (and possibly Glossaryck. Nothing's been confirmed involving him yet) Toffee now intends to execute the final phase of his plan. To regenerate his physical form and kill Mewmanity, starting with Star and the royal family.