Players signing up for Moshi Monsters can choose to adopt one of six monsters: Furi, Poppet, Diavlo, Zommer, Luvli and Katsuma. After customising their monster, players are free to roam around Monstro City, exploring the different environments and meeting the different characters who live there, as well as other players. Within Monstro City are a number of areas where minigames can be played, such as the Puzzle Palace or the Power Station. Completing minigames each day rewards the player with the in-game currency Rox, which can be used to buy food to feed their monster to keep it happy, or items to decorate their house.
One of the most popular aspects of the game are the collectible Moshlings. Players can buy seeds for flowers of different types and colours from a stall in Monstro City which can be planted (three at a time) in the garden outside their house. If the player comes back the next day they will find that the plants have grown, which will attract a Moshling to the garden if the combination of plants is correct. For example, to attract Chop Chop the player can plant any three dragon blossoms. Some Moshlings are harder to attract or require more specific flower combinations than others, and some Moshlings can only be collected during missions (see below).
Paying subscribers to Moshi Monsters have access to a number of extra features. On becoming a subscriber, a player receives their Moshi Passport, which allows them to get into a number of areas that free members can't get to, including The Port, Gift Island and the Underground Disco. In addition, they are allowed to change their monster's colouring, build extra levels onto their house, and see all the Moshlings they have collected in their Moshling Zoo.
The most significant bonus of being a member is becoming a Super Moshi and going on Missions.
Subscribers to Moshi Monsters can take part in Missions; episodic story-driven content focusing on the story of the evil Dr. Strangeglove and his plans to capture all the Moshlings. Missions play out much like a simple adventure game, with the player exploring new environments, talking to NPCs and solving puzzles by combining items. In addition, in each mission the player will be assisted by a new Moshling, which will be added to their collection.