Noxious Moss Hexmallow

Marshmallow Magic This marshmallow has an earthy, mossy flavor with a tangy hint of kiwi. After eating it, it turns your tongue green for a few minutes.
  You can use a bonus action to eat this marshmallow, when you do, your abilities, attacks and spells ignore any resistance to Poison damage a target may have until you finish a long rest. However, for the duration you also are vulnerable to Poison damage. If you are resistant, you lose the resistance. If you are immune, you become resistant. For the duration, you cannot gain the benefits of any other hexmallow.