Allay

java

The allay is a passive mob that resembles the vex which is able to fly. Its function is to assist players with the transport of items.

Pillager outposts
Allays can be found surrounding pillager outposts, confined inside dark oak cages. 1 to 3 allays can spawn in each cage.

Woodland mansion
Allays can also spawn inside jail cells within woodland mansions. 1 to 3 allays can spawn in each cell.

Behavior
Allays have a luminous texture, allowing them to be seen clearly in the dark. They fly around aimlessly until given an item. It will appear to hold that item in its hand and will scan the area around the player for examples of that same item, where it will then return it to the player. A player will get the item back if an allay is interacted again while the player has an empty inventory slot.

An allay has only one slot on its inventory, allowing it to carry 64 stackable items at once. An allay can carry a single non-stackable item, excluding the one that it holds. If a nearby note block is being played, the allay will instead return items to that particular note block for up to 30 seconds with a vibration particle reaching the allay. It will search for items around the note block.

When an item is given to the allay, they search for 60 blocks around the player. They can follow a player from up to 1024 blocks away. Allays have an item pickup delay, which means they can't pick up items immediately after they throw them.

When killed by other players or mobs, allays drop the items they were holding. Allays cannot be damaged by their owners. If they are damaged, they activate panic mode, where they will start moving faster and will have more random movements. If they have a Totem of Undying equipped, the Allay will be able to use it and gain a second life, similar to a player.

Trivia

 * Despite not having any connection with the warden and sculk sensors, they have a similar property when they interact with a vibration signal when a note block is being played.
 * Despite their ghostly appearance, allays aren't considered undead mobs, similar to ghasts and vexes.
 * Unlike vexes, allays cannot pass through blocks and are also not immune to fire or lava.