The Void Warden: The Ender Dragon's Right Hand Man

Concept: This is a rare mini boss that can be found in end cities or ships. This can be spawned by using the similar mechanics as trial chambers.

Combat: It has mechanics similar to that of a warden, considering the fact that it is located in the end, It has the ability to teleport behind you, it can also levitate with the help of shulkers in case the player tries to use an elytra

Reward: It drops the Sound protection enchantment which enables players to resist the warden in the ancient cities to a certain extent.

Lore: As the ancient builders used the stronghold and the end portal to escape from the warden, this can show players that the warden might have followed the builders into the end dimension