If you draw nightmists entire deck, which is entirely possible as much as she draws, and then only play heedless lash, with a master of magic in play, would she be able to play heedless lash over and over, dealing infinite damage? It works as far as I can figure, any objections?
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Revealing does not force a reshuffle, so even with all Heedless Lashes on the top of the deck, the last revealed one will not reveal any cards, thus will either do nothing or you could draw it into hand.
Master of Magic only heals upon playing a card, Heedless Lash puts a card into play, so only the first Heedless Lash will heal her.
Also, if a card puts another card into play, the first card will remain in play until the second card has completed its effects. If that second card also puts a card into play, then the first 2 cards will still be in play until the third card has finished.
You can of course continue the chain every round however, as long as you only ever draw 1 card, thus reshuffling the trash and gaining a Heedless Lash. But she will deal more damage to herself than she is healing, thus not being able to do it every turn for very long, unless your goal is to do it until she is incapped.