It never sleeps. It has to keep moving because if it stopped, its magma body would cool and harden.
A common sight in volcanic areas, it slowly slithers around in a con stant search for warm places.
These group to gether in areas that are hotter than normal. If it cools off, its skin hardens.
Molten magma courses throughout SLUGMA’s circulatory system. If this POKéMON is chilled, the magma cools and hardens. Its body turns brittle and chunks fall off, reducing its size.
SLUGMA does not have any blood in its body. Instead, intensely hot magma circulates throughout this POKéMON’s body, carrying essential nutrients and oxygen to its organs.
— Pokédex entries (via PokeAPI)