Anti Tarrasque

Ooze Squeeze. The Anti Tarrasque can fit through spaces up to 0.1 foot in width and cannot be Grappled or Restrained by any physical object.

Mobility. The Anti Tarrasque can move after it attacks on its turn instead of before, and cannot provoke opportunity attacks. It can also climb walls and ceilings and is unaffected by difficult terrain.

Corrosion. When anyone makes a physical attack against the Anti Tarrasque or touches it, the attacker takes an invariable 40 Acid damage, and the weapon gains a -1 to all rolls made with it until repaired. The attacker is also Grappled, and takes 20 Acid damage at the start of each of their turns until they use an action to make a DC 22 Dexterity check to free themselves, as the Anti Tarrasque only gets stronger the more brute force you try to use to escape it (A Strength escape is DC 27). The Anti Tarrasque can also eat through up to 5 times its size level (Same as how Explosion works) square feet of any material on its turn.

Explosion. When the Anti Tarrasque is destroyed, it explodes, and any creature within 5 times its size level (Tiny = 1, Small = 2, and so on) feet of it is affected as if they were hit by 2 Ooze Lash attacks. Additionally, everything within that area is coated with the ooze from the Leap legendary action.

Ooze Lash. Melee Weapon Attack: +20 to hit, reach 20 ft., 1 target. Hit: 32 (4d10+10) Acid damage. The attack also corrodes armor, reducing the AC bonus by 2 until repaired, and it also reduces the AC bonus of a creature's natural armor by 2. The range of this attack increases by 5 ft for every level of size this creature has, so a Tiny Anti Tarrasque reaches 25 ft, a Small one reaches 30, and so on.

Expand (Recharge 5, 6). The Anti Tarrasque increases its size by one stage. Anything caught inside of it is Grappled by it.

Split. When the Anti Tarrasque takes any Slashing, Piercing, or Bludgeoning damage, it splits into two Anti Tarrasques one size smaller. If the Anti Tarrasque is Tiny sized, this does not work. Only one of the pieces of the Anti Tarrasque grapples the attacker due to the Corrosion trait, and which one does so is chosen by the DM.

The Anti Tarrasque gets 3 legendary actions, which recharge at the start of each of its turn.

Leap. The Anti Tarrasque leaps 20 ft in any direction. The location it was previously at is now marked with Corrosive Sludge. Any creature that touches the Corrosive Sludge that does not have immunity to Acid damage takes 20 Acid damage instantly on touching it and must make a DC 16 Dexterity saving throw or lose the rest of their turn. At the start of their next turn, they can repeat the saving throw to unstick themself.

Absorb. The Anti Tarrasque absorbs or is absorbed by another Anti Tarrasque within 30 ft of itself. The Anti Tarrasque that remains heals HP equal to the amount the Anti Tarrasque that was absorbed had and increases its size by one stage.