Whenever an Oath is swore to Master of Mysticism and Metal, you may search your library for an equipment or aura, reveal it, and add it to your hand. Shuffle your library afterward. (Master of Mysticism and Metal is swore an Oath, if Master of Mysticism and Metal's was the target of a creature taking an Oath).
See Oath Test. If a creature can take an oath, and the oath targets, can creatures be swore Oaths? What's the wording to make receiving an Oath work? I originally had "Whenever ~ receives an Oath, you may search...," but swore sounded more flavorful.
The next problem is parasitism, so maybe make a mechanic that simply cares about being targeted instead: a heroic tweak that goes off of abilities targeting rather than just spells?
Receiving an Oath is parasitic though.
"is sworn"
The problem with triggering unrestricted of being targeted by abilities is that abilities can be free or as good as free. It's too easy to do and go infinite with it. One of the reasons heroic does not trigger from abilities.
I think you could change this to something like the equivalent of "When ~ becomes the target of an ability of a creature you control, that was triggered by that creature entering the battlefield". It's a mouthful, but it would include "Take an Oath".