...so, why is this bird so different from a typical Northern Pintail? Is it a hybrid, and, if so, what is it hybridized with?

The bill on this bird lacks the grays of an adult male Northern Pintail, and the face and neck pattern are somewhat muted. The barring on the sides isn't anything like what is typically seen, and the tertials are the wrong color, but the length and shape of them look mostly normal. The long tail isn't quite as long as it should be, and the color of the undertail is pale instead of black. This photo was taken in January, so we aren't dealing with some weird eclipse plumage.

Pintails WILL hybridize occasionally, but what combo could this possibly be?

Click here for an explanation: https://pbase.com/ternvomitthief/image/173210913