Onslaught was planned to appear in Beau DeMayo’s removed tenth episode of X-Men ’97 season 2.
DeMayo said Marvel removed his planned episode and rewrote the remaining season. In his version, clues throughout the season would have built toward Onslaught’s arrival in episode 10, alongside material inspired by the 1995 comic storyline Age of Apocalypse.
Onslaught is a powerful psychic entity created from the darker aspects of Professor Charles Xavier and Magneto. In the comics, that combination turns their shared psychological trauma and ideological conflict into a separate villain. The character became central to Marvel’s 1996–97 Onslaught crossover, which involved the X-Men, Avengers, and Fantastic Four.
The planned episode should not be confused with the season’s released Apocalypse storyline. Apocalypse is the season’s principal threat, while Onslaught belonged to DeMayo’s discarded version of the season. Mojo, Mister Sinister, and Nimrod are also major X-Men antagonists, but none was identified as the removed episode’s intended centerpiece.