Growing up in a number of orphanages and foster homes in New Jersey, Sidney Green was a boorish, clumsy child, often the target of cruel bullying by children and adults alike. An inveterate bed-wetter, Green carried around with him the funk of uncleanliness, which further ostracized him and made him miserable. Green's attempts to curb his nightly emissions by avoiding liquids led to dizziness and dehydration. Once his mutation manifested, a blissful drought beneath the waist set in, and there was a lack of sodden sheets. When Green joined Xavier's he was put in Gambit's Squad. As a student at the Xavier Institute, Green had regained some confidence, forwarding audacious advances to aesthetically stirring female student Foxx. When Foxx was exposed as Mystique, Green sensed betrayal and attacked her. Within days, Green was able to walk again. Yet, the experience of being smashed in the head with a flush-lavatory triggered unfortunate memories of his childhood, perhaps permanently traumatizing him.
Onyxx was seen captured alongside his fellow students in Limbo.
Onyxx was a mutant with a craggy granite body with the following abilities:
- Superhuman Strength
- Resistance to Physical Injury
- Onyxx's real name has only been revealed in the X-Men: 198 Files reference material.
- Onyxx was originally planned to be killed off in New X-Men Vol 2, but writers Christopher Yost and Craig Kyle were not allowed to. As Yost bluntly put it: "I hated that character." Later, however, he was killed of in X-Force Vol 3.
- 25 appearance(s) of Sidney Green (Earth-616)
- 3 appearance(s) in handbook(s) of Sidney Green (Earth-616)
- 1 minor appearance(s) of Sidney Green (Earth-616)
- 1 mention(s) of Sidney Green (Earth-616)
- 1 mention(s) in handbook(s) of Sidney Green (Earth-616)
- 16 image(s) of Sidney Green (Earth-616)