Mallard ducks have been known to hybridize with other duck species, on occasion. The hybrids are sometime referred to as "manky" ducks and people have often named the different manky varieties! Here are two mixed duck pairs at Lake Murray in San Diego.
A Mallard drake and a Duclair duck. The duclair is probably a hybrid between a mallard and the white Pekin duck.
An Indian Runner drake and a female mallard.