Animal Corruption

This spell lets you assert your necrotic will over a beast that you can see and convert it into an undead servant. Choose a beast that you can see within range. It must see and hear you. If the beast's Intelligence is 4 or higher, the spell fails. Otherwise, the beast must succeed on a Wisdom saving throw or be charmed by you for the spell's duration. If you or one of your companions harms the target, the spell ends. The creature dies when the spell comes to an end.

For the duration of the spell, the best is considered an undead ally.

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