Observed

The Observer is a hostile entity that does not attack. It follows players across land and observes them, and the observed effect is a visual indicator that carries debuffs. Each observation point adds to the effect, so more observation means faster drain and heavier debuffs, which players must deal with until the effect drains away. Observers drop a pool of potent poison behind any they are attacked near, and melee combat is the suggested approach unless the player stays well above or below the observer.

The mod is client and server, so the server and every player need it, and it requires Curios API. Observed is published for Forge only, for 1.19.4 and 1.20.1, with 1.4 for 1.20.1 as the latest file. The code is open source under the MIT License. Its design is inspired by the Barotrauma watcher, and the author lists potential spoilers in a linked note.