Greyroumon is an Ultimate level digimon whose name is derived from Greymon and rou, the Japanese word for wolf. His design is derived from Aguroumon and Greymon. Greyroumon shares many similarities with Aguroumon; in fact, their body structures are nearly identical. The only differences are that Greyroumon is much bigger and has the head of a Greymon rather than an Agumon. Through the Crest of Loyalty, PrehistoricGreymon digivolved and embraced his icy nature rather than his fire powers. As such, he considers ArchaicGreymon both a rival and a close friend. Greyroumon will remain loyal to everyone he cares about and becomes disappointed if they don't return that loyalty. Despite this, he will never stop helping his friends. The Crest of Loyalty appears on his shoulders.
During Double-Crested Warriors, AntiVolatilemon discovered a way to disable Matthew's and Brittani's Crests. PrimitiveAgumon and Haku lost the ability to reach their natural Ultimate and Mega levels, so they relied on DNA digivolution at first. When Gennai reminded the Digidestineds that they each had two Digi-Eggs that didn't match any of the original nine Crests, they realized they had one more Crest somewhere. Matthew and Brittani were able to keep this secret from AntiVolatilemon and his antimatter clones until their digimon had each achieved their new Ultimate forms. PrimitiveAgumon reached his second Ultimate level during a battle against Blossomon. Matthew was determined to not let Blossomon hurt his friends, but when Brittani and Haku were being held and PrehistoricGreymon was losing, Matthew was about to give up hope. Then he remembered his duty as a DigiDestined and his loyalties to his friends and PrehistoricGreymon digivolved into Greyroumon, who freed Brittani and Haku and defeated Blossomon.
Greyroumon becomes PrimitiveAgumon's preferred fighting form and remains so until his Mega form through the Crest of Loyalty is achieved.
Tundra Tornado- summons a tornado made entirely of snow to circle the opponent
Howl of the Hunter- releases a howl that strikes fear into the opponent and freezes them in place
Absolute Zero Ice Claw- takes a swipe at the opponent with his claws. Wherever contact is made, the opponent cannot move until it warms up