I once had a Beige Dragon that showed up as an opponent. The PCs had been beating the tar out of some thieves when one of them offered a map to a Dragon's lair in exchange for his life. He made sure to stress the creature's massive hoard. The PCs were more than happy to pounce on a plot hook and took the deal.

What they didn't know is that Beige Dragons are creatures of supreme mundanity and boredom. So when they got there they found the Dragon was not home, but that his horde consisted entirely of an extensive stamp collection, knitted tea cozies, old comic books, and newspaper clippings. It was just a massive cavern full of worthless stuff that only the Beige dragon would be interested in.

Then he came home and started blasting them with his breath attack, which was actually him droning at them in a monotone so diabolically boring that it knocks you unconscious.

They spent two days trying to escape the cave only for the Dragon to notice them leaving and start prattling on about his collection or something.

When they did get away the first thing they did was track down the rogue they got the map from and kill him horribly.

<3