Just like Darkwing Duck/Negaduck, Catboy/Night Panther, Owlete/Dark Owl, Spiderman/Venom, Danny Phantom/Dark Danny, Vengance/Ghost Rider, Ladybug/Missfortune, Chat Noir/Chat Blanc and more. Prince Poltergeist and Angelic Swan would have an evil version of themselves
 

 
In this case: Prince Poltergeist would be known as King Specter. An evil spirits commander whose powers are way more dangerous, his attire changes in aspect and colors. His ghosts companions, Guv and Betty change to a vicious and dreadful look and renamed Shock and Wrella
 
And as for Angelic Swan, she would be known as Malbatross. A demonic amazon themed after an Albatross, she can create destructive hurricanes and summon the hellish albatros spirit, her attire is almost different from her heroic self, the veil looks shorter, ripped and is black colored
 
 
It would be any reason that they got corrupted; Mind Control, Corruption, Hawk Moth’s akuma influence, Romeo’s opposite ray, etc. But whatever it is, they would be hard battle