Dungeons and Dragons. Tasha's cauldron of everything.
(Book)

"For use with the fifth edition of Player's handbook, Monster manual, and Dungeon master's guide"--Page [4] of cover.

"The wizard Tasha 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 them for the enrichment of all! Baked into this book are rule options for all the character classes in the Player's Handbook-- including new subclasses. And the book is sprinkled with the archmage's musings on everything from her wizardly rivals to the nature of the multiverse"--adapted from page [4] of cover.