The Fridge Monster was an alien-like creature that attacked the Bebop crew.
Spike Spiegel bought a Ganymede rock lobster in 2070 and stored it in the ship's attic. He forgot about it, and, over the next year, a monster was born. It was a small, black blob that slid around on the floors, walls and ceilings. It traveled very quickly and could alter its shape as it moved. It could incapacitate a living creature by biting it, secreting a toxin, although it was unknown if the bite was fatal or not.
It first attacked Jet Black, then Faye Valentine, Ein and Spike. They each developed a purple rash and fell unconscious. Spike was the only one left. Using a heat sensor, nets and grenades, he tried to kill it with no luck. Instead, he pushed the entire fridge out into space. As he did so, the creature attacked him, rendering him unconscious in the final moments.
It was unknown whether the monster had any effect on Ed, however, due to Spike setting the auto-pilot to land on Mars, it is possible she most likely succumbed to the monster's poison, too.