Duma's Apostle appears as an opponent in the Duma's Ordealsamiibo dungeon. An Apostle also appears in an optional skirmish in the Fear Mountain Shrine, which is necessary if one wishes to proceed further within the dungeon.
See class growth rate for more details on the mechanics of class growths in each game.
Class skills
Duma's Apostles are equipped with a passive skill that marks it as a flying unit. All members of the Duma's Apostle class also have the Nullify Ailments skill, although that skill is not technically tied to the class.