- Main article: Species
Cassette Beasts is a monster-taming game. The game is played in a third-person view.
After completing the main story, a permadeath mode (similar to Pokémon Nuzlocke rules), where beasts that are defeated permanently die in the playthrough, and a map randomizer, to increase replayability, are enabled.
The game's battle system is based around the player transforming into different beasts to battle each other. The game initially offers the choice between "spooky or sweet" for their first beast choice. Beasts can randomly encountered in the overworld, or are harnessed by rival combatants. The player can then "record" these beasts to add them to their party,
Attacks and other moves are based on different stickers, which can be transferred between different beasts. Beasts can be fused to gain extra strength, which combines both beasts into a more powerful one that shares the stickers of both.
Combat operates on a type-based system, where different monsters have differing types that react in different ways.
- Main article: Abilities
New Wirral, the game's overworld, is an open world, featuring various puzzles, chests, and other interactive features. A few select monsters grant special abilities which the player can use outside of combat to explore new parts of the island. The player can receive quests from people in Harbourtown and also can receive rumours on where to go next.
The plot of the game follows the player's character as they wake up on the beach of New Wirral, which they were transported to from their home universe. The main quest of the game, Land of Confusion, revolves around the character attempting to return to their home, as they are helped by other stranded people who are also stuck on the island.
A variety of partners are available throughout the game, and the player can strengthen their relationship with them by battling alongside them, completing their quests, and talking to them at a campfire while resting.