Undead Ally

You temporarily animate a corpse to fight alongside you. The corpse must be a CR ¼ or lower creature. If you target a creature with a higher CR the spell fails. The creature is brought to a state of undeath and is returned to its maximum hit points. The creature retains its stats and abilities however it is now an undead creature, cannot speak (however it knows the languages it knew in life), and gains immunity to poison damage. After 1 minute or when the creature is reduced to 0 hit points it dissolves into a pile of ash and cannot be raised again.

On each or your turns, as a bonus action, you can mentally command any undead you have created with this spell if it is within 60 feet of you (if you control multiple creatures you can command any or all of them at the same time issue the same command to each one). You decide which action the creature will take and where it will move on its next turn, or you can issue a general command, such as to guard a particular chamber or corridor. If you issue no commands, the creature only defends itself from hostile creatures. Once an order is given the creature continues to follow it until its task is complete.

At higher levels: When you cast this spell using a spell slot of 3th-level or higher you can animate higher CR creatures. ½ CR when cast with a 3rd level spell slot, CR 1 when cast with a 5th level spell slot, and CR 2 when cast with a 7th level spell slot.