You must have a Leomon, Ninjamon, Frigimon, or Whamon in your city to get Mamemon. Get your Digimon's HP up to 3000, MP up to 5000, Offence up to 500, Defence up to 300, Speed up to 400, and Brains up to 400. It is also Possible that your digimon 's happiness must be at the maximum.