ThunderGreymon is PrimitiveAgumon's fourth Armor form, whose name and design are based on thunder and Greymon. He appears similar to the original Greymon with several differences. His skull helmet is an electric blue with yellow lightning bolt markings. Blue lightning bolt markings appear on his shoulders, sides, and thighs. ThunderGreymon wields two lightning bolt-shaped javelins, given to him by Jupitermon himself, which are miniature versions of his master bolt. The Crest of Friendship appears on his chest.
After discovering the Digi-Egg of Friendship, Matthew and Brittani both used it to Armor Digivolve their digimon to combat the "fake" Armor digimon Volatilemon used to guard it. They were all defeated by an attack from ThunderGreymon and Hakuroumon, prompting the Digidestined to worry about why they were so easy to beat. ThunderGreymon suggested that they shouldn't worry because it wouldn't be difficult to get the Digi-Eggs back if all the guard digimon were like this.
Grey Lightning- shoots several lightning bolts from its chest
Jovian Javelin- throws both lightning bolts at the opponent, which come back to his hands when he summons them