Minecraft Dungeons:Phantom

The Phantom is an enemy-like mechanic that appears at night.

Night is similar to the feature in the base game of the same name, except, it comes when a player is defeated in multiplayer. The players will see near their utility bar a message telling them when the night will hurt them, accompanied by a timer. When the timer expires, phantoms will swoop down and attack any living players until night is chased away, by reviving the defeated player(s). Other than being added for logical reasons, the phantom is not actually a mob that you can fight, and is immune to all attacks. The only way to defeat it is the aforementioned way of reviving all defeated players.