Mammon/Relationships

Fizzarolli
While the two have yet to be shown interacting, the newspaper in "Oops" refers to Fizzarolli as "favored" by him, but the words following are blocked off so what Fizzarolli is favored for is not known.

Lucifer Morningstar
Mammon claims that he is friends with Lucifer. It is currently unknown whether or not Lucifer is aware of Mammon's self-proclamation of their "friendship" or affirms it.

Asmodeus
While not having been shown together it is implied in "Oops" that Mammon has a close relationship with his fellow Deadly Sin, with Asmodeus calling him by a familiar nickname, "Mam", when discussing the Greed Ring with Fizzarolli.