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"