Consume

Target one creature (that has 0 hit points and is still alive), spell or object within eyesight. If the target is a creature or spell they (the creature or the spell’s caster) must make a saving throw DC 10 + your Con modifier. On a fail, the spell or creature is consumed granting the caster 10 (3d6) hit points. If the target consumed is a spell gain temporary resistance to the damage type of the spell for 1 minute or until a new spell is consumed.

At higher levels. When casted at  4th level or higher you can choose to forgo gaining resistance and instead deal 1d6 of the selected damage type on your next attack.