Cofagrigus is a blue and yellow sarcophagus-like Pokémon with red, menacing eyes and four ebony hands that appear to be shadows. A simply designed face, which is the mask Yamask carries, is prominent on the "forehead" of the Pokémon. Its real face is covered up by parts that slide open when it is active. White, sharp fangs create a taunting smile, and flamboyant patterns veil the coffin. The coffin is said to be made of solid gold.
Ancient legends once told Cofagrigus could seal nearby humans in their bodies and turn them into mummies; grave robbers who mistake them for normal coffins get this fate. Cofagrigus is said to have once been human but having forgotten its memories from when it was alive. They also enjoy eating gold nuggets. It lives in tombs and ruins waiting for victims. Cofagrigus has been used as a symbol for the wealth of kings from a bygone era.
Previously, due to the censor that prevents Pokémon with offensive nicknames being traded on the GTS, an English language Cofagrigus could not be traded without a nickname in Generation V due to having the slur "fag" in its name. However, the filter has since been altered to allow Cofagrigus to be traded without a nickname.
Cofagrigus's design seems to be based on a sarcophagus. It was also most likely based on supposedly cursed Egyptian tombs. Any trespassers in the tombs are said to fall under a "curse" from its owner, which is said to cause illness, serious injury, or death. The hype of cursed tombs was made popular when many people in a team of explorers in 1922, who had opened and entered King Tutankhamun's tomb, began dying after the exploration. Cofagrigus's MummyAbility, which passively turns other Pokémon into mummies that in turn transform other Pokémon into mummies, is very similar to the popular culture depiction of the spread of a "zombie virus" in horror films.