Mamemon is the Partner Digimon of Player (Digimon World) (Mameo).
The Player starts with either an Agumon or Gabumon. After he defeats Analogman and Mugendramon and returns back to the Human World his Mamemon calls him back to the Digital World as Analogman has returned.
Many years later, Mameo's Mamemon is suck in a Digitama because of the BH Program. After the defeat of Tsuzuki Shoma and Omegamon Alter-B Mamemon is reborn. After Titamon joins the City it uses its power to summon Mamemon from the future to fight alongside its past self and summons a Mugendramon. Mamemon and its future self fight against the -next 0rder- Protagonist, however they are defeated.
The events are the same as the original -next 0rder-.