Swarm.
The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny insect. The swarm can't regain hit points or gain temporary hit points except with "My Empress" reaction
Swarm Weakness. While Antioch is resistent to most single target attacks, being a swarm doesnt protect him from area attacks. When Antioch is hit with an Area of Effect Attack, Antioch takes an extra amount of damage from the AOE equal to the number of damage dice it has (so Fireball with 8d6 will deal and extra 8 damage). In addition Antioch cannot use Swarm Guard to protect from an AOE damage spell.
Spellcasting. The [Swarm that Walks] is a 7th-level spellcaster. Its spellcasting ability is [wisdom] (spell save DC 15, +7 to hit with spell attacks). The [Swarm that Walks] has following [druid] spells prepared:
Cantrips (at will): [Infestation], [Poison Spray], [Thorn Whip]
1st level (4 slots): [Fog Cloud], [Speak with Animals] 2nd level (3 slots): [Enlarge Reduce], [Wither and Bloom], [Summon Beast]
3rd level (3 slots): [Conjure Animals], {Dispel Magic], [TIdal Wave] 4th level (1 slots): [Giant Insect], [Polymorph] [Blight]
Engulf. The Swarm that Walks is made up of vicious insects that gnaw and devour any living matter the Swarm desires. When the Swarm occupies another creatures space, the Swarm Automatically inflicts it's Devour melee attack and inflicts damage. This damage can only be done to each creature once per turn.
Devour. Melee Weapon Attack: +7 to hit, reach 5 ft., 1 target. Hit: 10 (2d6 + 4) [piercing] damage.
Larvae Dart. Ranged Weapon Attack: +7 to hit, range 30/60 ft., 1 target. Hit: 16 (4d6 + 4) [piercing] damage. When the Larvae Dart hits a creature, the Larvae attempts to burrow into the target at the end of the targets turn. Unless removed by an attack (any damage kills) or a DC 10 Athletics Check, the Larvae will burrow inside and explode, dealing it's damage again automatically. Requires a Recharge from a D6 only recharging on a 6
Swarm Casting. The Swarm that Walks is made up thousands of pieces of the casters soul, and only part of the swarm are required for the casting of a spell. The Swarm that Walks can cast any spell or cantrip requiring 1 action as a Bonus Action. This ability is however lost when the Swarm is reduced to half it's HP or Lower
Swarm Guard. The Swarm that Walks knows that the Queen or King of the Hive must be protected no matter the sacrifice of those beneath it. When the Swarm that Walks is hit with an attack, once per turn the Swarm can force an ally within 15ft of the attack to intercept and take the attack in it's stead. The exception to this is the "Perfectly Ultimate Great Moth" which is too valuable even for Antioch to risk it's safety over his own. See "My Empress" Below
My Empress. Antioch the Swarm that Walks values the Perfectly Ultimate Great Moth above all. When the Perfectly Ultimate Great Moth Hatches, Antioch shifts tactics to protect his Empress above all others. When the Perfectly Ultimate Great Moth enters the battlefield, Antioch recharges any reaction already used this turn, and sacrifices all other Insect and Insect Creatures alive including summons, regaining 10 HP for each one as Antioch devours them all. For the rest of the combat Antioch loses "Swarm Guard" and can then on each future turn use his Reaction to intercept an attack targetting the Perfectly Ultimate Great Moth so long as Antioch is within 30 ft of the Perfectly Ultimate Greath Moth. This reaction also ends the Swarm Barrier Legendary Action
Swarm of Locusts (Costs 1 Actions). Antioch is a master at Manipulating his Swarm, allowing him to cast a cantrip of his choice when he uses this legendary action.
Swarm Barrier (Costs 3 Actions). Antioch temporarily dismisses his Walking Form to form a Barrier using his own body. In this state Antioch Cannot Attack, Cast Spells, or use any action outside of his Reactions. Antioch forms a sphere around the Caccoon for the Perfectly Ultimate Great Moth, blocking line of sight to the Caccoon and protecting it from harm. Antiochs AC is treated as 10 in this state. Antioch can choose to end this form on his turn or when the Caccoon Hatches and triggers "My Empress"
Description
When a powerful spellcaster with a strong personality, a lust for life, and a remorselessly evil soul dies and is buried in a graveyard infused with eldritch magic, a strange phenomenon sometimes occurs. The flesh of the decaying body fats and instructs the very worms that gnaw, and these graveworms quicken not only on corruption but upon the spellcaster’s memories and magical power. The spellcaster’s very soul is consumed in this vile process, only to be split apart to inhabit each of the individual chewing worms in so many fragments. The result is a hideous hive mind of slithering life known as a worm that walks—a mass of worms that clings to the vague shape of the body that granted it this new existence, and can wield the powers and magic the spellcaster had in life. A worm that walks retains memories of its life as a spellcaster before its death, but is not undead—it is a hideous new form of undulant life.
Variant, The Swarm that Walks. Because of the odd and usually accidental circumstances through which worms that walk are born, the process of such birth is far from standardized. Thus, the worms themselves can take more shapes than simply the most common one. Antioch Hacekamo died in the swampland where flies, locusts and wasps all congregated, and when they feasted on his Corpse his own inate magic and deep sated hatred of his fellow man, caused him to rise once more as A Swarm that Walks
Antioch as a Swarm is a being made up of tens of thousands of insectoid beings all containing a piece of his soul. Unless every single one is destroyed, he could regrow and reform at a later date. Because of this Antioch is treated as a swarm and follows the rules in 5E for Swarms, as well as containing powerful druidic magics. Though Antioch on his own wasn't a master of magic, his plans and experiments are to create an insectoid being far more powerful than he himself, and in doing so will ushur in a return to the Golden Age of the Planet where Insects ruled.