“ An evil ruler got the idea of mixing a trampoline and a gallows together. As long as the one to be hanged bounces on the rubber trapdoor it won't open, but bouncing gets very tiring after a while.”
“ A city is being plagued by a swarm of winged mice. The vermin can get anywhere, and they can easily avoid their normal predators by simply flying away from them.”
“ If you want to add a 'supernatural' touch to your campaign, define the rules of magic and the universe. Make your players comfortable with those rules. Then your new supernatural creatures must then break those rules.”