Nowadays marfantes are mythological beings similar to ghosts used to scare children from the Baix Ebre and Montsià areas of Catalonia, but they actually existed in a specific moment of history.
They were ordinary people who wrapped themselves in a blanket to hide their identity and moved around at night to commit an action that went against the law or was considered immoral (often visiting a lover, or to scare people away from where a friend was having relations with a lover), and managed to be undisturbed by scaring the locals who might see them. Under the blanket sometimes they had other objects to make their appearance harder to recognise, such as a long hook to seem taller.
In the 1940s, the years of generalized poverty after the Civil War (1936-1939), people who smuggled food also used this costume.
Source: Inventari del Patrimoni Cultural de les Terres de l’Ebre