"Extra life" is a healing artifact that is found in a can with a large jagged letter 'M' on it. These cans are sometimes dropped by monsters possessing an abundance of vitality. Though it's unclear exactly where the metal that forms the can itself comes from.
When the contents of these cans are drunk, the imbiber gains 40 to 80 hitpoints. Heroes and heroines are frequently reluctant to use these cans. They claim it's because they are forgetful, but they just don't want to admit that they sometimes might rather die than taste the vital essence of a monster.
Occasionally heroes and heroines claim these artifacts fail. But this just means they poured the foul brew out onto the ground rather than drink it.