Monster Fun Grimoire
Possibly alternatively known as the Bumper Fun Grimoire, this text is reputed to contain the last truly original joke known in the Universe. Therefore various groups have an vested interest in keeping it firmly under lock and key. (The Fools would not be too happy about any truly original humour seeping out into the world, for instance. Regard their position on unauthorised new jokes which have not gone through the several hundred-years long process of authorisation by the Guild council, and the necessary period of practical refinement into the approved form of words).
It is thought that the Trickster-God had a hand in the production of this grimoire, so you have been warned.
Ninth or tenth generation expurgated copies which have been approved for everyday use by wizards are still closely guarded, but are believed to be a compendium of near-lethal practical jokes combined with practical exercises in, for instance, the re-combination of common household substances in order to make fireworks. (which the text does not tell you are also highly explosive until after you have assembled, mixed, and struck a match... it's that sort of grimoire)
While fireworks are the traditional province of wizards, it could well be that today all this comes under the heading of "dabbling with science", which worries wizards as it raises issues of demarcation, and you know how the alchemists come down on that sort of thing if they catch you doing it...
Monty Python's Flying Circus did an extended sketch on the Funniest Joke in the World, which turned out to be so deadly (people died laughing) that it was translated into German and used as a weapon of war. The jokes in the MFG are very likely to have a similar effect.