Alchemical Undead

Undead Fortitude. If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.

Aversion of Fire: If the Alchemical Undead takes fire damage, it has disadvantage on attack rolls and ability checks until the end of its next turn.

Immutable Form: The Alchemical Undead is immune to any spell or effect that would alter its form.

Lightning Absorption: Whenever the Alchemical Undead is subjected to lightning damage, it takes no damage and instead regains a number of hit points equal to the lightning damage dealt.

Magic Resistance: The Alchemical Undead has advantage on saving throws against spells and other magical effects.

Death throes: When the alchemical undead dies, it explodes releases a corrosive ichor, and each creature within 20 feet of it must make a DC 12 Dexterity saving throw, taking (2d6) acid damage on a failed save, or half as much damage on a successful one.

Multiattack: The Alchemical Undead makes two melee attacks.

Slam: +7 to hit, reach 5 ft., one target. Hit: (1d6 + 1) bludgeoning damage.

Acid spit: +4 to hit, reach 30ft., targets within a 10ft area Hit: (2d4 + 2) acid damage