Haunter is a purple Pokémon with a gaseous body. It has a round head with a pair of disembodied hands. Each hand has three pointed fingers. Its head is flanked by three large, spiked protrusions on either side, and its eyes are large and triangular with small pupils. The gasses composing its head curve down to form several sharp teeth framing a pink mouth and a long tongue. Its body tapers into a jagged tail.
Haunter hides in very dark places, where it plots to take the life of the next living thing that comes near it. It then silently stalks its victim and licks it in order to steal its life force, killing it by inducing continuous shuddering. It has the ability to float through solid walls. Despite its predatory nature, it has been known to entertain and prank people in the anime, and even been shown to intense feel loyalty to a deceased Trainer. Haunter lives or near graveyards and dark, abandoned caves.