Mordenkainen's Tome of Foes

Mordenkainen's Tome of Foes details the great cosmic conflicts of the D&D multiverse: the Blood War between devils and demons, the eternal struggle of the elves, the long memory of the dwarves, the gith schism, and the strange duergar of the Underdark. It provides extensive lore plus stat blocks for over 140 creatures and NPCs, including new high-tier threats. Written in the voice of the archmage Mordenkainen, it is a goldmine for DMs running epic campaigns.