SkullGreymon

Technically the first ever Ultimate Level Digimon owned by a DigiDestined, this Digimon was the result of Greymon Digivolving for the wrong reasons. This Digimon was uncontrollable and the only good that came from this was it showed the DigiDestined not to misuse the power of their crests. Later appeared in Season 2. His attacks are Dark Shot and Double Dark Shot.

Attacks

 * Dark Shot : Fires the fish missile on his back.
 * Double Dark Shot: Fires 2 fish missles from his back.

Digimon Adventure
When Tai wanted Greymon to Digivolve to beat Etemon's Greymon, it caused Greymon to Digivolve to SkullGreymon and easily defeat it. He also attacked Birdramon, Garurumon and Kabuterimon before reverting back to Koromon.

Digimon 02
When the Digimon Emperor took over Greymon with a Dark Ring, he wanted him to Digivolve in MetalGreymon but he instead turned into SkullGreymon and defeated the Meramon, Flamedramon, Halsemon, Digmon and a bunch of DarkTyrannomon before reverting back to Agumon as the Digimon Emperor made off with him. No matter how much he tried to get Greymon to Digivolve to MetalGreymon, he turned into SkullGreymon until Agumon's recapture and the introduction of the Dark Spiral turned Agumon into a Virus version of MetalGreymon.

Digimon Tamers
A SkullGreymon was among the many Digimon seen through the rip in the sky during Vikaralamon's rampage.