Divine Smite

When you hit a creature with a melee weapon
attack, you can expend one paladin spell slot to
deal radiant damage to the target, in addition to
the weapon's damage. The extra damage is 2d8
for a 1st-level spell slot, plus 1d8 for each
spell level higher than 1st, to a maximum of 5d8.
The damage increases by 1d8 if the target is an
undead or a fiend.