Horde Overlords are huge beasts from the netherworld of the Abyss, the leaders of The Horde, and loyal servants of Yama. You will be required to have high-grade equipment and powerful spells to beat those in 1 on 1 battle. However, the rewards are just insane including rare wearable NFTs, unique skills, and even new playable characters!
Horde Overlords usually appear at the end of the level in certain Play Modes like Dungeons, Castle Defense and Battle Royal. More on the Play Modes was mentioned in the dedicated section of this Gamepaper.