Dear Tai-won (and whoever else is interested),
about your question if Herod's swearing by "Mahound" in the mystery plays
is an instance of medieval "orientalism": in the mystery plays, it's quite
normal for all sorts of bad characters to swear by "Mahowne" or "Mahound".
Especially Herod and Pilate do it. This is of course a reference to
Mahomet, who was, in the eyes of the medieval playwrights, _the_ typical
"heathen god", not especially oriental, but also the god of heathen
peoples in the Old Testament. There is no connection with the Islamic
prophet or even the orient in general. At the same time, they saw him as
identical with the devil.
For more information, see vol. 2 of the new Early English Text Society -
edition of the Towneley Plays, notes concerning Play 9, l. 9; 16/1; 24/69.