The real end boss

After you defeated Maschindramon at Mt. Infinite, go all the way up again where you fought it and you will suddenly see a new digimon there.

A Digitamamon will be there suddenly.

It has completly maxed stats and therefore is the strongest enemy in the game, so be prepared!

After defeating it it will join the city and helps at the restaurant.

(This encounter is completely optional and only needed if you seek the medal for 100 prosperity)