Butterfly

Flashing Insanity. If a creature sees the butterfly, it must make a DC 21 Wisdom saving throw, taking 6d8 Psychic damage on a failed save, or half as much damage on a successful one. If the creature fails its saving throw by 5 or more, it goes permanently Blind until restored by a Greater Restoration spell or other magic. If a creature succeeds on the saving throw, it becomes immune to the butterfly's Flashing Insanity for the next 2 minutes. If a creature fails the Flashing Insanity saving throw, it must make a DC 21 Intelligence saving throw or be Charmed by the butterfly for 10 minutes.

Force Field. The butterfly is inside a 5x5x5-foot Forcecage that follows it wherever it goes and only blocks attacks coming in and not attacks coming out, meaning the butterfly is essentially protected from outside harm but can still move around and attack you. If the forcecage is destroyed, it comes back on this initiative next turn.

Lightning Aura. On the butterfly's turn, it can choose any number of creatures within 30 feet of itself to take 10 Lightning damage. Those creatures must make a DC 18 Dexterity saving throw or be paralyzed for 1d4 minutes. On a successful save, the creature is immune to the butterfly's Lightning Aura paralysis for the next 1 minute, but will still take Lightning damage. If a creature fails its saving throw against the paralysis, it must make a DC 18 Constitution saving throw, taking an additional 40 Lightning damage on a failed save.

Flyby. The butterfly does not provoke opportunity attacks.

Legendary Resistance (5/day). If the butterfly fails a saving throw, it can choose to succeed instead.

Heat Death. The butterfly unleashes a blast of fire hitting everything within 60 feet of itself, igniting flammable objects. If an object is destroyed by this fire, it explodes in 30 feet around itself doing 6d6 Fire damage. The main kaboom does 10d6 Fire damage, and if you are within 30 feet of the butterfly the damage rolls have advantage. Also, anyone hit by the main fire must make a DC 24 Dexterity saving throw and a DC 24 Constitution saving throw. If the Dexterity saving throw is failed, the creature will take 5d6 extra Fire damage and become Paralyzed forever until something is done to reverse it. If the Constitution saving throw is failed, the creature is Blinded and Deafened for 10 minutes and NOTHING can cure this, and every turn while Blinded and Deafened in this way the creature takes 3d6 Necrotic damage.

Black Hole. The butterfly opens up a black hole on any spot that it chooses. The black hole is 60x60x60 feet and anything the butterfly doesn't specifically choose to not be affected within 300 feet of the edge of the black hole without sufficient protection will get pulled 50 feet towards the black hole every second. While inside of the black hole, at the start of a turn of a creature inside it, the creature takes 8d8 typeless damage and must make a DC 15 Constitution saving throw or be sent to a plane of existence of the butterfly's choice, typically Death Dells, the Far Realm, or Sholo-Tovoth. This happens automatically if the black hole reduces a target to 0 hit points. The black hole lasts for 3 minutes. A creature killed by this disappears from existence and can only be recovered by a Wish spell.

Decay Ray. The butterfly fires off hundreds of beams of pure entropy around itself, causing any creature the butterfly doesn't specifically avoid shooting within 150 feet to lose 30 max health, take 30 damage, lose 3 of every stat, plus all armor and weapons get a permanent -5. If this reduces the health, max health, or any stat of a creature to 0, that creature gets erased and is not remembered by anyone. Anyone who is hit by this attack and survives suffers a random one of the effects of the Contagion spell.

Fluttering Death. The butterfly spawns 10 tiny Aberrations known as Fluttering Deaths. It can spawn these wherever it likes. Fluttering Deaths have 6 in every stat, 20 AC, 20 HP, 200 feet of fly speed, and do 10 Fire damage to anything that touches them. They can launch blasts of fire on their turn that do 10 damage, with a range of 100 feet. Additionally, when a Fluttering Death dies, it creates an explosion similar to the Fireball spell.

Holy Eruption. The butterfly manipulates the energy of higher powers into a devastating blast of holy celestial force. This is fired as a 15-foot wide 300 foot laser. Anyone in the area must make a DC 21 Dexterity saving throw, taking 10d8 Radiant damage on a failed save or half as much damage on a successful one. Regardless, anyone struck by the beam must also make a DC 18 Charisma saving throw, taking 6d8 Psychic damage on a failed save, or half as much damage on a successful one. If a creature is reduced to 0 hit points by this attack, they are Petrified even if they survive.

Time Erosion. The butterfly manipulates time to cause the wears of age on every creature of its choice within 120 feet. Anyone affected by this must make a DC 21 Strength saving throw, aging 8d8+10 years on a failed save, or half as much on a successful one. They also gain 1 level of Exhaustion regardless, and lose 3 Strength, 3 Dexterity, 3 Constitution, and must make a DC 18 Intelligence saving throw or lose 3 Intelligence as well. Additionally, the victims of this attack also take 8d6 Necrotic damage, and if they failed the Strength save, they must make a DC 17 Charisma saving throw or become affected by Madness.

Eldritch Visage. The butterfly flashes an illusion of an incomprehensible eldritch being that destroys minds that see it. Any creature that sees the illusion must make a DC 23 Wisdom saving throw or take 10d10 Psychic damage and roll a d4, and on a 1 or a 2 they are Stunned for 1 minute. They take 5d10 Psychic damage instead if they succeed on the save. If they fail the saving throw by at least 5, they are affected by an effect similar to the Confusion spell. Additionally, after failing the save, regardless of how much they failed by, they must make a DC 21 Intelligence save or be subject to the effects of Feeblemind.

Body Disruption. The butterfly uses its magic to manipulate the bodies of up to 3 creatures of its choice within 60 feet. Those creatures must make DC 23 Constitution saving throws, taking 10d8 Force damage on a failed save, or half as much damage on a successful one. Regardless, the creature is Stunned for 1 minute. If a creature is reduced to 0 hit points by this attack or while stunned by it, its body is transformed into a CR 2 Gibbering Mouther controlled by the butterfly. Anyone who witnesses this transformation must make a DC 18 Wisdom saving throw or take 4d6+10 Psychic damage and be knocked unconscious from fright and shock.

After its action on its turn, the Butterfly can take one bonus action. It cannot take the same one two turns in a row.

Dragon Warp. The butterfly sends a creature within 200 feet of it to a plane of existence containing nothing but the creature and a shadow being with the exact same statblock as an Ancient Red Dragon, and the plane of existence is the dragon's lair. The warped creature cannot escape this plane by any means, regardless of interplanal travel, unless the dragon is killed. When the dragon is killed, the creature returns to where it was before it got warped and is immune to Dragon Warp for 1 minute. If another creature is Dragon Warped while there is already a Dragon Warped creature, a new dragon dimension is created.

Tentacle Vines. The butterfly summons 3 Huge tentacles from any nonliving surfaces it wants within 300 feet, as long as the surface is large enough for the tentacle. These can each make 3 melee attacks per turn on creatures within 20 feet of them, and no more than one attack per tentacle can be on the same target. The tentacles attack immediately after being summoned and then every turn on the butterfly's turn. These melee attacks have +10 to hit, 6d4 Bludgeoning damage, and a reach of 15 feet. A tentacle can only be removed by hitting it with at least 50 Fire damage done in one attack, or by ripping it out of the ground with a DC 18 Strength check. Anything else is ineffective. Instead of attacking with a swing attack, a tentacle can choose to attempt to grapple a target, requiring the target to make a DC 21 Dexterity check to avoid the grapple. If they fail to avoid it, they are Grappled by the tentacle (Escape DC 22). While a target is grappled, the tentacle can only make one melee attack instead of three, but it does 6d4+10 Bludgeoning damage instead of 6d4 and does it to both the target of the attack and the grappled target. If it doesn't do this attack, the tentacle can squeeze a creature it is grappling, doing 6d6 Bludgeoning damage. If a creature attempts to escape a tentacle's grapple and fails, roll a d4. On a 1 or a 2, that creature gains 1 level of Exhaustion. Tentacle Vines are immune to all status conditions.

Energy Drain. The butterfly evenly splits 10d6+30 Necrotic damage between all creatures of its choice within 60 feet. Any creature hit by this must make a DC 20 Constitution saving throw, and if they succeed, they only take half the damage. If they fail, they are under an effect similar to the Slow spell for 5 minutes. If they fail the saving throw by 5 or more, they gain 2 levels of Exhaustion and take 3d6 Psychic damage. After this attack is used, the butterfly heals equal to half the total damage done by the attack.

Control Mind. The butterfly unleashes an invisible ray of potent magical mind energy at a creature of its choice within 90 feet. That creature must make a DC 20 Charisma saving throw or be completely controlled by the butterfly until either the creature or the butterfly is reduced to 0 hitpoints or a different mind control magic is used against it. The creature can repeat the saving throw at the start of each of its turns, ending the effect on itself on a success. Once this is done, that creature becomes immune to the butterfly's Control Mind for the next 1 minute. A creature has disadvantage on the saving throw against this spell if it is charmed by the butterfly.

Shield. Until the start of its next turn, the butterfly rolls a d4 for every attack made against it. On a 1 or a 2, the attack is completely nullified.

Refraction Storm. If the butterfly is hit by an elemental attack, 25% of the damage the attack does is taken by the attacker instead of the butterfly. This happens before resistances and immunities are taken into account. The butterfly can also choose up to 2 other creatures in addition to the attacker to also take the damage.

Divine Ultimate. Any creature that attempts to hit the butterfly with a melee attack that does not get blocked by the force field will get hit by a lash of extreme radiant power, doing 6d6 Radiant damage to that creature and forcing it to make a DC 18 Wisdom saving throw. On a failed save, the attack fails and the creature is knocked Prone.

The butterfly has 5 legendary actions, which recharge at the start of each of its turns

Control. A creature currently under the effect of the butterfly's Control Mind bonus action performs an action.

Teleport. The butterfly teleports to somewhere it can see within 300 feet. It cannot do this if it currently has a Prismatic Sphere from its Mythic Hurrah ability.

Vine Attack. A Tentacle Vine created by the Tentacle Vines attack gets to perform an action.

Force Burst (Costs 2 Actions). The butterfly fires a blast of force out of itself. Every creature within 200 feet will take 8d8+20 Force damage and must make a DC 23 Constitution saving throw or be knocked Prone. If the butterfly choses, it can knock all creatures hit by this attacks, pushing them 30 feet further away from the butterfly.

The butterfly, upon reaching 100 HP, enters its immensely powerful mythic form and uses its attack, Mythic Hurrah, immediately. It also gains access to its other mythic actions, which are basically additional legendary actions.

Mythic Hurrah (1/day). The butterfly loses its forcecage shield in favor of a Prismatic Sphere, a spherical prismatic wall that follows the butterfly around just like the shield does. It regains the forcecage if the sphere is destroyed. It cannot regenerate the sphere. While the sphere is surrounding it, the butterfly's speeds are all reduced to 90. The butterfly also gains regeneration which lasts for 1 day, giving it the ability to regenerate 3 HP every initiative count. Upon activating Mythic Hurrah, the butterfly also gets to use 2 of its bonus actions. It can even use the same one twice.

Lightning Blast. The butterfly fires a bolt of lightning at a creature within 300 feet of it. This attack rolls to hit and has a +7 to do so. The creature that is hit takes 8d8+10 Lightning damage. Even if the attack misses, the creature still takes damage, only half as much. A creature that is the target of this attack, even if it missed, must make a DC 19 Dexterity saving throw or be paralyzed for 1d4+1 minutes.

Act. (Costs 2 Actions). The butterfly gets to use one of its regular actions.