Nightcaster Arkvarius II was a half-Anodite, half-Oneiromancer from Ledger Domain. He was the son of Nightcaster Arkvarius I and the brother of Murmadan Arkvarius. Throughout his life, he fulfilled the legacy of his father by assuming his father's identity as he sought to destroy Azmuth.
He first appeared in Hit and Miss.
- In Hit and Miss, he battled his way into Azmuth's headquarters on Galvan Mark II and kidnapped him as Ben was unable to stop him. He later left a hypnotized, transformed version of Eunice fight Ben in his place.
- In Ten Plus Twenty, he fought Ben in the middle of Downtown Bellwood and lost at the hand of both Obsorber and Nigester, who was removed from the Omnitrix for being a possible gateway for Nightcaster back to life. He was accidentally killed by Ben in the same episode when Nigester dealt a powerful blow to his fragile body.
- Nightcaster II takes after his father's Oneiromancer side more than his brother since his body proved to be far more fragile in his final battle with Ben.