Bolster Undead

You suffuse an area with negative energy to increase the
difficulty of harming or affecting undead creatures.
Choose up to three undead creatures within range.
When a targeted creature makes a saving throw against
being turned or against spells or effects that deal radiant
damage, the target has advantage on the saving throw.

At Higher Levels. When you cast this spell using a spell
slot of 2nd level or higher, you can affect one additional
undead creature for each slot level above 1st.