This a list of unseen characters who exist within Danny Phantom, but have not properly appeared in the series.
Grandpa Fenton is the grandfather of Danny and Jazz Fenton. He was only mentioned once, in "Splitting Images," by Danny when he entered the Ghost Zone for the first time, "It's like I dropped into Grandpa Fenton's yearbook."
Judging by his son, Jack Fenton's story from the first episode Grandpa Fenton had lived in a log cabin in Farmer City, Illinois with his family. He had discouraged his son from wanting a pony as the family had to eat horse meat during a war. These details could possibly be untrue as his son has a love of rambling.
However a known detail about him (besides the Ghost Zone looking like his old yearbook) is he has a ancestor from the Salem Witch Trials who looks very much like his son, John Fenton Nightingale. John's obsessiveness towards the supernatural - in this case witches - and Jack's obsession of ghosts implies paranormal contact runs in the family.
Jasmine the cat
Jasmine the cat is Jack Fenton's cat in the alternate timeline of "Masters of All Time." Earlier in the same episode, Jack remarked that he thought the name "Danny" was dumb, revealing that it was probably Jack who named Jazz and Maddie who named Danny.
Ricky Marsh was a student that Tucker once blamed for throwing up in Sam's lunch, when Tucker himself was actually the culprit. Sam apparently kicked Ricky off the monkey bars for what she thought he did. In "Splitting Images," Danny uses this story to convince Sam and Tucker that it is him, and not Sidney Poindexter.