Minecraft wiki entry for Command_blocks_and_functions, associated text: This is a reversed version of Destroyer. /execute as @p at @s run fill ~1 ~-1 ~1 ~-1 ~-1 ~-1 grass_block‌[Java Edition only] or /execute @p ~ ~ ~ fill ~1 ~-1 ~1 ~-1 ~-1 ~-1 grass‌[Bedrock Edition only]. This puts a 3×3 grass square under a player.