Majora's Mask 3D: Fast Rupees
Yes, you can enter and re-enter the room for 60-80 rupees each time to great effect. Sorry I suck at holding my 3DS still while playing it.
How it was done: this was in the first room of the Ancient Ikana Castle interior, where the ceiling directly above had already been bombed in with a Powder Keg. This let light into the room, which was reflected onto the ReDeads with the mirror shield on my back for an instant kill. Wearing Garo's Mask makes them dance around uselessly instead of attack you. Hooray for rupees!
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