Necromancers Shadow

A mob is marked for capture when it is killed while a sculk totem is held in the main hand or the offhand. The soul is stored as a small entity that displays soul particles at the spot where the mob died. Right-clicking that entity with the totem summons a ghostly shadow of the original mob. The stored shadow also appears as an item in the inventory tooltip of the totem, and it is lost if the player dies.

Summoned shadows keep most of the behaviour of the original entity, but they lose their hostility and flee from players. Extra data on the entity is saved again when a shadow despawns, so the shadow keeps that data in its next form. The mod also covers boss mobs, with the Ender Dragon, Wither and Warden named as examples of mobs that work. Necromancers Shadow requires Fabric API and is published for Fabric only, across six release versions 1.21.5 – 26.1, under the MIT License, which makes it open source. The server and every player need the mod installed. The author notes that compatibility with other mods has been tested, but results are not promised.