Spot-billed Ducks, from Asia, have three subspecies: the Indian, Chinese and Burmese. The Indian Spotbill (A. poecilorhyncha poecilorhyncha), above and immediately below, has lighter plumage and small red spots at the top base of bill (larger for males; inconspicuous for females); it also has a green speculum. The Chinese Spotbill (lower down page) is darker/browner, no red spots at base of bill and a blue speculum. Both have bright orange legs.
The Chinese Spotbill - darker than the Indian, no red spots at base of bill and with blue speculum. (Pacific Black Duck has similar face and plumage but plain black bill, green speculum and much lighter yellow legs.)
This bird has the bill pattern for the Chinese Spotbill but the body feathers
are wrong and the head seems too dark -- looks like a hybrid with Mallard?