Grumblemon is a servant of Tactimon & Lilithmon, the dimwitted sidekick of Etemon.
Grumblemon is rather excitable, & may act like an eagar child when Lilithmon has a plan, or when the DigiDestined are having trouble in a battle. Grumblemon is easily frightened by his bosses' bad tempers. Grumblemon is a coward &, rather than fight, he along with Etemon, will accompany MadLeomon, Minervamon, & other Digimon as they attack the Earth & cheer them on. However, he often goes to Earth when there is no fight going on because his main duties are acting as a spy & saboteur.
Grumblemon later leaves the moon with Tactimon & Lilithmon when they flee from the Machine Empire.