Ungeziefer Kaiser

The Unwrapped Present: The Roach Emperor cannot be affected by enemies inflicting roll debuffs or buffs against it. Attacks that must target a single target recieve -2 to hit or to their criteria when targeting the Roach Emperor. When successfully hitting a target, lose 1 Sanity. 
"Are there really no more wrappings underneath?"

The Emperor's Subjects: Gain 50 Protecting Roaches on turn start. For every turn the Roach Emperor spends in battle, it gains 3 less Protecting Roaches, to a maximum of 20 reduced Protecting Roaches. Lose 1 Protecting Roaches for every 5 dice of damage this unit takes from an attack. 
If all Protecting Roaches was lost in the last turn of combat, take 20% more damage from attacks for a turn. After this turn, continue gaining Protecting Roaches.
"They crawl out unheralded from betwixt all the lines that form where walls meet."

The Emperor's Mantle: On turn start, gain Protecting Roaches x 40 bonus health.
"The Legion of Roaches moves for no one but its Emperor"

The Emperor's Legion: When hitting a target successfully, inflict 3 Hurting Roaches. Then, for every dice of damage inflicted on the target, inflict 1 more Hurting Roaches. At the start of every turn, all Hurting Roaches expire on targets, doing 1% of the target's max HP per Hurting Roaches.
"Rip, seep, trickle, carve, tear, devour."

The Emperor's Blood: Take 50% less damage from all non-physical or magical attacks. Cannot feel pain or have disadvantage imposed on skill checks. When below 50% HP, all attacks -2 to hit.
"'Become dulled and inured to all things'"

The Emperor's Wrath: When below 50% HP for the first time, activate the Mythic Form Uncontrollable Metamorphosis.

Suddenly, One Day: When Morph is triggered on a target, roll 1D6. Results are as follows: 1 = the target takes an additional 1D4+2 burning damage, 2 = the target will take 1D4+2 damage from bleeding the next time it takes an action, 3 = the target must pass a DC8 dexterity check or be knocked prone, 4 = the target will take an additional 1D4 true damage the next time they are hit, 5 = the target gains a -1 to hit the next turn, 6 = for the next turn, the Roach Emperor gets a +1 to hit.

A Wing's Decisive Weapon: The Roach Emperor can take two actions every turn.

The Emperor's Whip & Fist: Melee Weapon Attack: +14 to hit, reach 25ft, 1 target. 8 (2D6+2) slashing damage, 8 (3D4+2) bludgeoning damage. Trigger Morph twice on its target. The Roach Emperor gains +1 to hit on its next attack. The Roach Emperor forms its arm into a thorned whip and slashes as its opponent before forming it into a mace and crushing its target.

The Emperor's Devouring: Melee Weapon Attack: +14 to hit, reach 15ft, 1 target. 14 (2D8+6) bludgeoning damage. On hit, absorb all buffs and conditions the target may have. This includes things like Bardic Inspiration, additional roll bonuses, etc. Halves the Hurting Roaches on its target. The Roach Emperor forms its arm into a massive maw and crushes its target between them.

The Emperor's Quaking: Melee Weapon Attack: +14 to hit, reach 20ft, 7 targets. 11 (3D6+2) bludgeoning damage. After the attack, the targets must pass a DC14 dexterity check or be knocked prone. For every dice that did not roll 1 in damage, increase the difficulty by 1. The Roach Emperor forms its arm into a club, striking its targets before turning it into a heavy mace and slamming the floor.

The Emperor's Flogging: Melee Weapon Attack: +14 to hit, reach 25ft, 7 targets. 10 (2D6+4) slashing damage. Inflict 1 Morph on the target. On use, gain 10 Charge. After the attack, consume 5 Charge and all targets must pass a DC12 dexterity saving throw or take an additional 2 damage per Charge the Roach Emperor has. The Roach Emperor forms its arm into a multi-tongued thorned whip before speedily slashing at its targets.

March of Roaches: Ranged Weapon Attack: +14 to hit, reach 30ft, 1 target. 8 (3D4) piercing damage. For every 2 Hurting Roaches on the target, do an additional 2 damage. For every dice that did not roll 1 on the attack, inflict an additional 2 Hurting Roaches on the target. The Roach Emperor commands its army to move forth and march, releasing a horde of gnawing roaches that bite and tear at the target.

K...kill... kill me...: As a reaction, Gregor can fight against the Roach Emperor's metamorphosis. He must pass a DC20 wisdom saving throw, gaining +1 per lost 5 Sanity. If he successfully passes this check, the Roach Emperor gains disadvantage to hit and -5 to damage for the turn. 

The Roach Emperor has access to 3 legendary actions, which can be taken after another creature's turn. These charges reset at turn start.

The Emperor's Whip: Melee Weapon Attack (costs 1 legendary action): +12 to hit, reach 10ft, 1 target. 12 (2D10+2) slashing damage, triggers 1 Morph on the target. The Roach Emperor forms its arm into a thorned whip and slashes at its target, grasping it and crushing it.

The Emperor's Fist: Melee Weapon Attack (costs 1 legendary action): +13 to hit, reach 10ft, 1 target. 10 (4D4+2) bludgeoning damage, triggers 1 Morph on the target. The Roach Emperor forms its arm into a mace and throws it at its target before reeling it back and smashing them with it. 

The Emperor's Hungering: Ranged Weapon Attack (costs 1 legendary action): +12 to hit, reach 35ft, 2 targets. 8 (2D6+2) piercing damage, triggers 1 Morph on the target. The Roach Emperor releases a swarm of roaches that bite at its target.

Uncontrollable Metamorphosis: As the Roach Emperor feels its mortality, it begins to mutate rapidly and uncontrollably, adapting to its surroundings and granting it even more power.

The Emperor's Excision: Melee Weapon Attack (costs 1 bonus action): +8 to hit, reach 15ft (+10 to hit for every 5 dice of damage the last attack the Roach Emperor suffered), 7 targets. 18 (4D6+6) bludgeoning damage, deal an additional 20 damage for every 5 dice of damage the last attack the Roach Emperor suffered. Inflict 2 Morph on the target. The Roach Emperor grows its arm to a long claw before slashing at its targets, cutting into them before tearing the claw away.

The Emperor's Feast: Melee Weapon Attack (costs 1 action): +9 to hit, reach 15ft (+10 to hit for every 5 dice of damage the last attack the Roach Emperor suffered), 1 target. 10 (2D8+2) bludgeoning damage, do an additional 20 damage for every 5 dice of damage the last attack the Roach Emperor suffered. If successfully hitting its target, remove all of the target's bonus health and do 1 damage to them, not including the additional damage. After the attack, the target gets a -2 to hit for their next attack and heal by 20HP. The Roach Emperor forms its arm into a giant maw before clamping down on its targets, chomping repeatedly before retrieving the arm.

'Son, don't forget to go for the heart.': Melee Weapon Attack (costs 1 action): +14 to hit, reach 25ft, 1 target. 20 (5D6+5) piercing damage. triggers 4 Morph on the target. If this attack does not successfully hit its target, the Roach Emperor will take 50% more damage next turn. This attack counts as a criticial hit if it rolls a nat 17+. If the attack hits the target, 6 surrounding targets must make a DC16 dexterity saving throw or take 50% of the damage. The Roach Emperor forms its arm into a claw before quickly piercing the hearts of all the surrounding people in rapid succession.