Five Rainbow Buddhas

Five Rainbow Buddhas (五色如来) are a group of bosses from YGGDRASIL.

Background
The Five Rainbow Buddhas are among the World Enemies created by YGGDRASIL developers for groups of players to encounter and face in battle.

The Dark Warrior Arc
During a discussion with the Swords of Darkness, Ninya brought up the likelihood of them facing dragons. However, her companions thought that scenario to be impossible as the chances of an encounter with dragons were very low. Still, it reminded Ainz about the World Enemies from YGGDRASIL.

Strength
Five Rainbow Buddhas are on the level of World Enemies. Their attack “Five Celestial Death Throes” could bypass resistances that the undead possessed.

Trivia

 * The Buddha apparently is a prevalent religious figure in the southern regions of the New World.
 * In the official English release of the second light novel, they were referred to as the "Five Transcendent Ones".
 * The Five Rainbow Buddhas could also be a reference to the Five Tathagatas or Five Great Buddhas, aspects of the Primordial Buddha. Oddly in Overlord: The Undead Oh!, Nishikienrai makes up a mass hallucination story at a student excursion about the Great Buddha of Nara and Great Buddha of Ushiku fighting in the city of Nara, which was also visited by the Great Buddha of Kamakura. The Great Buddhas mentioned are each a representation of the Five Great Buddhas: The Great Buddha of Nara depicts Vairocana, while the Great Buddhas of Ushiku and Kamakura depict Amitābha.