Amaranthine Gas is a dangerous substance found in certain caves in The Subspace Emissary. When characters enter the purple mist, they quickly start taking poison damage at about 2% every half-second. Characters do not flinch while in the Amaranthine Gas. The gas can be temporarily cleared by striking a nearby switch.
The gas from this game and Super Mario 64 have similar effects and appearances; both make players lose health when in it.