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Spaceman Spiff is pursued by a Muck Monster spacecraft.

The Muck Monsters of Mordo were aliens who attacked Spaceman Spiff while he was piloting his spaceship in the vicinity of Planet ZK-5. They fired a fatality-flare at Spiff which missed by mere micromips. They broke off from their pursuit when Spiff flew his ship into the rocky, icy rings of the planet.

The Muck Monsters themselves were not seen, only their spaceship in the distance as they pursued Spiff.

This encounter was apparently a metaphor for Calvin playing dodgeball in gym class with Moe.