"One Winged Angel - Final Fantasy VII" is a high quality rip of "One Winged Angel" from Final Fantasy VII.
The rip is a mashup / melody change of Psy's "Gangnam Style" and the advertised track.
The rip begins normally until 0:08, when a softer version of the "Gangnam Style" instrumentals cut in. The trumpets and other acoustics from "One Winged Angel" then play the melody of "Gangnam Style". The chanting in "One Winged Angel" is added at 1:16, shouting "Sephiroth" after "Gangnam Style"'s chorus.
The rip's joke is fully realized at 3:21, when PSY's vocals are added to sing the phrase, "Eh, sexy SEPHIROTH".