The wizard Tasha, whose great works include the spell Tasha's hideous laughter, has gathered bits and bobs of precious lore during her illustrious career as an adventurer. Her enemies wouldn't want these treasured secrets scattered across the multiverse, so in defiance, she has collected and codified these tidbits for the enrichment of all.
Baked into this book are rules options for all the character classes in the Player's Handbook, including new subclasses. Thrown in for good measure is the artificer class, a master of magical invention. And this witch's brew wouldn't be complete without its new artifacts, spellbook options, spells for both player characters and monsters, magical tattoos, group patrons, and other tasty goodies.