Ruby are monsters that exist in the Bubble Bobble Universe. They are cannons that fire teeth from their mouths that bite and harm the games heroes. They come in various different colours, each colour representing a different behaviour. The standard kind are a somewhat flesh colour.
- Spitting missiles with teeth on the end that hit and kill the player.
- Moving back and forth (blue versions only).
- Bubble Bobble 4: Friends
- Bubble Bobble Legend (unofficial fan-game).
- Bubble Bobble: Wistful Memory (unofficial fan-game).