Egyptian Osiris-Antinous
The marble Antinous at the Metropolitan Museum of Art depicts the young god with attributes of Dionysus, but this is by far not the only Antinous in existence. Although the Dionysian Antinous is by far the most common, there are also many more iterations showing Antinous with features of Osiris or Serapis, two Egyptian gods, or other Greek and Roman gods.
Antinous-Osiris at the Vatican Museums
Osiris is the Egyptian god of the dead, the underworld, and the afterlife, so it follows that Antinous be represented as him, since he died in the waters of the Nile, the territory of Osiris. He was one of the main gods in Egyptian mythology and religion.
Serapis is a Greco-Egyptian god whose cult was formed in order to unite the Egyptians under Greek rule to their leaders. Osiris was sometimes replaced by Serapis in different depictions during Roman times.
The Egyptian Antinous looks like images of pharaohs and other Egyptian sculptures. With the headdress that pharaohs wear, he appears regal and divine. While the Dionysus-Antinous at the Met looks more life-like and emotive in the manner of other Greek art, the Osiris-Antinous stands erect and still.
Both reflect the respective styles of their locations, because the Greeks (and, by proxy, the Romans) created statues in which the subject is in motion or appears that he might move. The Egyptian art style, on the other hand, is very straight and the subjects are almost always in the contrapposto position, with one foot forward. This position seems to be a normal way to stand, but it looks stilted and unreal when one looks at Egyptian art.
In Egypt, people kept their rich history of pharaohs and pyramids but experienced life as Roman citizens as well. The Antinous-Osiris type statue exemplifies this cultural mixing by portraying a Roman boy-turned-god as the ancient Egyptian god of the underworld. The different statues of Antinous reflect the regions from which they each came; the Antinous-Osiris were likely made in Egypt; the Greek/Roman Antinous-as-Dionysus were crafted in Greece and the Italian peninsula. Though records do not show from where the Met Antinous was made, it is more likely to have come from Italy or Greece than Egypt.