Permafrost

6th-level evocation

Casting Time: 1 bonus action

Range: Self

Components: V, S, M (white dragon scales worth 500 gp)

Duration: concentration, up to 1 minute

Classes: sorcerer, wizard

An icy chill passes over your body, giving you a better understanding of winter’s fury. For the duration, when you cast a spell that deals cold damage, you cause your target to become vulnerable to this damage type for the attack. When you cast any spells that deal cold damage to a target that is resistant to that damage type, you cause the target to lose their resistance to cold damage for the attack. When you cast any spells that deal cold damage on a target that is immune to this damage type, you cause your target to become resistant for the attack instead.