Caustic Lime Hexmallow

Marshmallow Magic This marshmallow has a tangy lime flavour with an incredibly sour aftertaste. It is dusted with bright green sugar, that sizzles on your tongue.
  You can use a bonus action to eat this marshmallow, when you do, your abilities, attacks and spells ignore any resistance to Acid damage a target may have until you finish a long rest. However, for the duration you also are vulnerable to Acid 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.