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.