A derivative of the Fire Shield
spell (both count as the same spell). Thin and wispy flames wreathe your body for the duration, shedding bright light in a 10-foot radius and dim light for an additional 10 feet. You can end the spell early by using an action to dismiss it.
The flames provide you with a warm shield (or a chill shield, as it's alternative suggests). The warm shield grants you resistance to cold damage (and the chill shield grants you resistance to fire damage).
In addition, whenever a creature within 5 feet of you hits you with a melee attack, the shield erupts with flame and the attacker takes 2d8 fire damage (or 2d8 cold damage from a cold shield).
a bit of phosphorus or a firefly
Protego di Incendo
Verbal Component (Alternative):
Mystic powers that I now wield, summon forth a burning/chilling shield.