A Ruin Kobold Sentinel is a red demi-human creature, with long, thin ears sticking out of their helmets and a big red tail. A large portion of its head and body is tightly covered and protected by metal armour, which makes the throat its only weak point. A Sentinel is armed with huge halberds in the light novels, and maces in the anime.
Sentinels aid Illfang the Kobold Lord as minions, adding further struggle for players to defeat the boss. They are so far the only known enemies seen fighting alongside a Labyrinth boss in the original Aincrad, most likely to make the fight more challenging to the opposing players as Illfang is weak compared to other high-level boss enemies. Because Sentinels are only found in the boss room, they are considered to be rare monsters.
As Sentinels are humanoid creatures, they are capable of using Sword Skills.