Minecraft wiki entry for Command_blocks_and_functions, associated text: This allows the player to destroy a cube of materials around them as they walk, using /execute. The command is /execute as @p at @s run fill ~1 ~2 ~1 ~-1 ~0 ~-1 air‌[Java Edition only] or /execute @p ~ ~ ~ fill ~1 ~2 ~1 ~-1 ~0 ~-1 air‌[Bedrock Edition only]. Use the repeating command block with the "Always Active" option selected, and the cube of air will be created wherever a player go. Basically, /fill takes out a specified amount of space, similar to /setblock, but it uses two coordinates and fills the space in between them with the material of the players choosing . In this case, that material would be air. Now, every time a player moves, it will fill a 3×3 cube of air around the player. A destroyer is great for enemy bases, or simply being a crazy griefer.