A Micromon is about the size of a marble, and sustains itself on an internal bacterial "battery" sufficient to power its minimal life functions for several cumulative weeks of active play before needing a nutrient infusion. They come in a variety of brightly-colored morphs; more recent releases positively bristle with tiny, nonfunctional bioweaponry, while early entries- the priciest on the market- resemble simplified versions of small, endearing retrofauna such as arthropods, but tend to have especially powerful and incongruously themed moves.

During gameplay, players take turns deploying Micromons onto the field and directing them to use "attacks" against opposing Micromons. All attacks are expressed via simple psigital messaging, which tracks each 'mon's HP, stats, and moves and communicates this information to onlookers at a glance. Besides their psigital capabilities, a Micromon's brain nodule is just sufficient to allow it to stand in place and rhythmically flex its appendages when deployed, and enter a curled-up inactive state when returned to the confines of a storage pouch or when its HP is depleted.

Micromons are manufactured en masse by breeding farms, which engineer prototypes with reproductive capability. Rarely, a standard 'mon will retain this ability, and when two such Micromons are kept in the same pouch, an egg may result, containing a muddy-colored, radially symmetrical clump of limbs that produces an unintelligible psychic hum in lieu of a description. These hybrids are not legal for play, but sell for a pretty penny.

Hacked Micromons exist that continuously express their psigital description at a very high "volume" when they are perceived by any means, creating an effective battlefield distraction. Modification of this sort is banned by all official Micromon tournaments.