Weasley Weapons

In the last chapter of my Harry Potter story I mentioned that Fred and George had some weapons so evil that they'd never even used then for pranking. I now have to describe them...

so far my best ideas are vampiric Pygmy Puffs ( basically blood-sucking fast breeding tribbles), turbo-nifflers (like ordinary nifflers but a LOT faster), and giant squid pheromone spray (not sure about that one since I'm not writing tentacle porn). Any other suggestions?