The barrier is weak because the Elves are not cleaning their neighborhood. When the Pixies try to spruce up, the Elves send two spiders to fight back.
The magical barrier is weakening because the Elves do not keep their neighborhood clean. The Elves respond to the Pixies' soap-water assault by doing magic on two spider mites, to make them become giants and invade Pixieville. The situation soon turns against the Elves and the Pixies will have to stop the spiders that are taking over the city.
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