Arcane Feast

You touch one willing creature, and magically mark it. Whenever a damaging spell targets a marked creature, the caster of the damaging spell must succeed a saving thrown of their spellcasting ability (DC 14), or deal half damage. If they fail, the marked creature gains a resistance to the triggering damage type until the end of the damaging caster's turn.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, whenever the damaging caster fails their saving throw, the marked creature gains 1d6 temporary hit points for each slot above 2nd