In variants that have vulnerability to elements, especially as a temporary debuff that the player can be inflicted with, you should be able to remove the debuff by doing something that would give you intrinsic resistance to that element (such as eating a corpse or tin).

Another possibility, not mutually exclusive, is that you should be able to stack multiple sources of the resistance to negate or reduce the severity of the vulnerability - i.e. two extrinsic sources of the resistance, or intrinsic resistance paired with an extrinsic.

When something has debuffed you to be vulnerable to a certain type of elemental damage, you should be able to eat a corpse or tin of a monster that conveys resistance to that type of elemental damage to cancel out the debuff.

MR should cut the duration of temporary elemental vulnerability that you get by having a monster cast it at you.