Allay

java

The allay is a passive flying mob similar to the vex.

Pillager outposts
Allays can be found surrounding pillager outposts, confined inside dark oak cages.

Woodland mansion
Allays can also spawn inside jails within woodland mansions.

Behavior
Allays fly around aimlessly until with an item. It will appear to hold that item in its hand, and then will scan the area around the player for instances of that same item, where it will then return it to the player. They have a slot in their inventory, allowing them to carry 64 stackable items at once.

Allays can pick up items that are 15 blocks away from the allay.

Allays can pick up variants of the item given to them.

If a 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.

They have a luminescent texture, allowing allays to be seen clearly in the dark.

Trivia

 * Despite not having any connection with warden and sculk sensors, it has a similar property when it interacts 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 can't phase through blocks.