A ghost block will be created when an enderman puts down a moving piston head block.

Steps to Reproduce:

1. Summon an enderman in an enclosed space
2. Modify what block it holds:

   execute as @e[type=minecraft:enderman] run data merge entity @s {carriedBlockState:{Name:"minecraft:moving_piston"}}
   

3. Wait for it to place the block
   (If it's taking too long, tick sprint the game)
4. Try and place a block where the enderman set down the moving piston head

Expected & Observed Results:

→ A ghost block will be present where the enderman placed it. Despite the block appearing to be air, the player will not be able to interact with the block postion.
→ The moving piston head would either not be allowed as something an enderman can hold, something it can't put down, or it would just be destroyed when placed.

Notes:

1. In previous versions, the piston_extension block has been used in Enderman anti-griefing command block designs, because they could previously not place them and would also not have any visual appearance.
2. Thee ghost block can be destroyed with TNT or /setblock