Divine Smite

Paladin feature
Attack Action | Melee | Instantaneous
When you hit a creature with a melee weapon
attack, you can expend one spell slot to deal
radiant damage to the target, in addition to
the weapons damage. The extra damage is 2d8
for a 1st-lv. spell slot, plus 1d8 for each spell
lv. higher than 1st, to a maximum of 5d8.
The damage increases by 1d8 if the target is an
undead or a fiend, to a maximum of 6d8.