Slugma is a limbless Pokémon composed of magma. Its body is bright red, fading to a duller red along its extremities. It has large, round, yellow eyes with small pupils. Slugma's head is ovoid with flame-like extensions spreading upward from its eyes and round, stable drops of magma dangling from its upper jaw. Its lower body is irregular in shape, and occasionally emits bubbles.
Slugma's circulatory system is composed entirely of magma, which delivers vital nutrients and oxygen to its organs. In order to prevent its body from cooling and hardening, Slugma neither sleeps nor ever stops moving. If its body does begin to cool, it will become brittle and may break apart. Slugma constantly seeks warm places, and gathers with other members of its species in mountains and volcanoes.
Additionally, while Murkrow and Houndour are catchable in Johto via the Safari Zone in Pokémon HeartGold and SoulSilver, the only possible way to get a Slugma before obtaining the National Pokédex in HeartGold and SoulSilver is to receive it from Primo as an Egg - it must otherwise be traded in or transferred from a Pokéwalker linked to a game which has already unlocked the National Pokédex.
Slugma has the lowest base stat total of all Fire-type Pokémon.
Slugma is based on a slug with a body of lava. It may also be based on the Cherufe, evil creatures of rock and magma that inhabit the magma pools found deep within Chilean volcanoes. Slugma's Shiny form may be based on cooled, hardened magma, which becomes a dark, metallic color. The form may also be based on solder, a liquid metal that is extremely hot and hardens when it cools, similarly to lava.