How about a chance in arcade clockwork gate level for the level to be in a sort of corrupted state. Where broken pixellated monsters would appear.
I'm thinking a really low chance that could offer some unique rewards upon completing. Perhaps a completely different soundtrack for these places similar to an old video game's "instrumentals" and odd resistances and weaknesses for the monsters that spawn there.

It would make the arcade seem more attractive and make knights want to explore it more if it had a unique monster or two.

Oh, and I'm thinking of something that isn't directly related to the swarm. Cousins, maybe?