These walls form a labyrinth with no exit for enemies.
Damage Gate lets you Special Summon a monster from the Graveyard with less ATK than the battle damage you took from an opponent's attack. With that being said, Labyrinth Wall has 0 ATK, so you can special summon it after taking any amount of battle damage.
You can guess an incorrect level to send Labyrinth Wall to the graveyard to set up a special summon.
Using this card's effect, you can set Labyrinth Wall face-down without needing any tribute. This will keep it hidden, making your opponent unable to switch the position and attack it first to flip it up.