Unholy Strength

Choose an Undead creature in range that is under your control. For the duration of the spell, the target deals an additional 2d6 damage with each successful melee attack.
At the end of the duration, the target's speed is reduced by 10ft for one round as it recovers from the overload of Necrotic energy.

At Higher Levels: When cast using a 4th level spell slot, you may target one additional Undead under your control for every 2 levels above 2nd.