Undead Armor. Bathax coats his body with Zombies to protect himself. Bathax starts any encounter with 80 temporary hitpoints. Whenever he takes 10 damage, a greater zombie falls off his body. When Bathax kills a creature. He can use an action to place their corpse on his body; gaining back 10 temporary hitpoints for each creature. When a creature hit's Bathax with a melee attack. The zombies attack; dealing 7 (1d6+5) slashing damage for every 10 temporary hitpoints he has to the creature.
Legendary Resistance (3/Day). If Bathax fails a saving throw, it can choose to succeed instead.
Regeneration. Bathax regains 20 hit points at the start of his turn. If Bathax takes fire or radiant damage, this trait doesn’t function at the start of its next turn. Bathax dies only if it starts its turn with 0 hit points and doesn’t regenerate.
Death Pursuit. Bathax can unerringly track any creature it has wounded in the last 24 hours, and it knows the distance and direction to its quarry as long as the two of them are on the same plane of existence.
Undead Fortitude. If Bathax is reduced to 0 hitpoints. He can make a DC 10 Constitution saving throw to be reduced to 1 hitpoint instead. The DC increases by 5 for each successful saving throw.
Shroud of Darkness. If Bathax is in dim light or darkness, attacks against him have disadvantage and his AC is increased by 5.
Leaching Critical. When Bathax scores a critical hit on a creature, he regains hitpoints equal to half the damage dealt.
Multiattack. Bathax makes two Rend attacks and one tail attack.
Rend. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 21 (3d10 + 5) slashing damage.
Tail. Melee Weapon Attack: +10 to hit, reach 15 ft., one target. Hit: 10 (1d10 + 5) bludgeoning damage.
Dreadful Presence. Bathax can force each creature within 60ft of him who can see him to make a DC 20 Wisdom saving throw or become frightened of him. A creature who is frightened of Bathax has their movement reduced to 0. A frightened creature can repeat the saving throw at the end of their turn in order to not be frightened. A creature who saves is immune to the effects for 24 hours.
Haunting Breath (Recharge 5–6). Bathax emits a 60ft cone of black miasma form his mouth. Each creature in that cone must make a DC 20 Constitution saving throw, taking 40 (8d10) Necrotic damage on a failed save, or half as much damage on a successful one. A creature who fails the saving throw becomes paralyzed until the end of their next turn.
Phantom Step. Bathax can become ethereal and teleport 30ft in a straight line. Each creature he passes through takes 5 (1d10) cold damage. Bathax cannot end his movement within a solid object.
Undead Command. Bathax can make one of his minions make an attack against a creature of his choice within their melee range.
Vengeful Strike. When a creature hits Bathax with an attack within 10ft of Bathax. He can make one rend attack against them.
Insite Failure. When a creature attempts to cast a spell or magical effect on Bathax within 120ft, he can use his reaction to force the creature to make a DC 20 Concentration check. If the creature fails, the spell is consumed.
Bathax can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Bathax regains spent legendary actions at the start of its turn.
Tail Attack. Bathax makes one Tail attack.
Rend Attack (Costs 2 Actions). Bathax makes one Rend attack.
Wing Attack (Costs 3 Actions). bathax beats its wings. Each creature within 10 feet of Bathax must succeed on a DC 18 Dexterity saving throw or take 8 (1d6 + 5) bludgeoning damage and be knocked prone.
Uncaged Souls (Cost 3 Actions) (1/Day). Bathax can summon a legion which consist of 2 skeletal knight, 2 ogre zombie, 4 skeleton, and 2 deathlock wight. All of Bathax's creatures have advantage on attack rolls and saving throws as long as they are within 60ft of Bathax.