SkullGreymon

SkullGreymon is the evil alter-ego/version of Greymon. If Greymon is mistreated, he will Digivolve into SkullGreymon.

Appearance
SkullGreymon is an alternate Ultimate form of Greymon. The "skull" prefix in his name refers to his body, which is completely fleshless and entirely composed of bone. He has a missile that lies on his back that is shaped like a shark, as well as red eyes.

Personality
SkullGreymon is extremely aggressive, destructive and uncontrollable Digimon whose violent temper causes him to have endless desire to fight.

Digimon Adventure 01
Tai desperately wanted Greymon to Digivolve further when he gained his Crest of Courage, an object that would help Greymon obtain his next level. When the evil Etemon confined Tai and the other DigiDestined children in a colosseum he forced Tai's Greymon to battle a wild Greymon (who had an upper hand during the fight). Tai purposefully threw himself in front of the evil Greymon to make his partner Digivolve. This caused Greymon to Dark Digivolve into SkullGreymon, who easily destroys the evil Greymon. However, he suddenly went berserk, attacked Birdramon, Garurumon and Kabuterimon, beat them very easily, started wreaking havoc, then fled the colosseum. Exhausted, he reverted to Koromon. This also happens in the Digimon book entitled Mimi's Crest Of Sincerity.

This experience shows how the mental state of a DigiDestined can affect the way his/her partner will Digivolve. Each of the DigiDestined in Adventure were bestowed personality traits (in Tai's case, Courage) that they had to display to unlock their Digimon's Ultimate levels. Counter to his trait, Tai had been exhibiting feelings of fear and helplessness during Greymon's battle, which caused Greymon to Digivolve into the wrong Ultimate.

Digimon Adventure 02
When the Digimon Emperor took control of Greymon with a Dark Ring, he tried to force Greymon to Digivolve into MetalGreymon, but instead Dark Digivolves to SkullGreymon once again. SkullGreymon defeated the new DigiDestined with just mere hits, however he managed to defeat one Meramon, some Airdramon and a big group of DarkTyrannomon and destroying a Control Spire with his Dark Shot. The Emperor took him back to his base in an attempt to trigger the correct Digivolution several times until he managed to get Greymon to become an evil version of MetalGreymon by using a Dark Spiral (created of 3 Dark Rings joined together).

Digimon Fusion
SkullGreymon was one of members of the Midnight Army, as one of the AxeKnightmon's minions. He attacks the Fusion Fighters and fights MetalGreymon. After he was defeated, he and SkullSatamon was absorbed by AxeKnightmon to gain their powers. It is unknown what happened to SkullGreymon when AxeKnightmon left the scene in the Dust Zone. It can be assumed that SkullGreymon and SkullSatamon were presumed destroyed.