Wanted to show off that yes, Duo has more than one mask and probably a while slew of them from over the years lol

Even tho it takes a lot for a godling to get sick, there are germs in Purgatory and Duo's very well acquainted with those germs. He is the building's pathologist after all. He doesn't want to bring anything home to himself or to Octo and he's like...the worst patient when he gets sick cause he thinks he knows everything and he complains a lot lol

He only wears the mask when he's in the lab working or going around any of the clinic rooms for whatever reason.