The Skeleton with a blue mask is Gas Sans. He wears a black gas mask obviously with a blue color in the middle and with fingerless black gloves and gray jacket, undershirt along with a lighter grey hood, he wears black pants and shoes overall. He seems very silent, in fact he can't even speak because of the smoke inside his 'lungs' being too thick. If he took off his mask, he will slowly die from not having the smoke circulate when he breathes.