Roleplaying Information.  Boxxy T. Morningwood is a mimic-turned-doppelganger hailing from a world in another sphere, where the laws which govern and define reality differ from those of Abeir-Toril.  Originally motivated purely by survival instincts, Boxxy has evolved into a cunning and ruthless engine of chaos.

Ideal: “Nobody touches my shinies.”

Bond: “There are three kinds of people in the world: me, my pawns, and my prey.”

Flaw: “Responsibility?  Guilt?  What are those?  Are they tasty?  They’re not?  Then I don’t need them.  Go bring me tasty things!”

Action Surge (2/Short Rest). Once per turn, Boxxy takes an additional action.

Adaptive Defense.  The first time each round that Boxxy is subjected to a damage type other than bludgeoning, lightning, piercing, or slashing damage, it gains resistance to the triggering damage type until the start of its next turn.  Boxxy can only resist one damage type per round using this trait.

Agent of Chaos (Luck).  Boxxy has 3 luck points and regains expended luck points when it finishes a long rest.  Whenever Boxxy makes an attack roll, an ability check, or a saving throw, or an attack roll is made against it, Boxxy can spend one luck point to roll a d20.  The luck point can be spent after the triggering roll, but before the outcome is determined.  Boxxy chooses which of the d20s is used for the roll.

Assassinate. Boxxy has advantage on attack rolls against any creature that hasn’t taken a turn in the combat yet. In addition, any hit Boxxy scores against a creature that is surprised is a critical hit.

Bane (Lightning). If Boxxy takes lightning damage, it must succeed on a DC 21 Constitution saving throw or be paralyzed until the end of its next turn.  This condition ignores immunity.

Biomass.  Boxxy counts as one size larger when determining its hit dice as well as its carrying capacity and the weight it can push, drag, or lift.

Butcher of Humanity (Fear Aura). Any humanoid that starts its turn within 20 feet of Boxxy must make a DC 20 Wisdom saving throw, unless Boxxy is incapacitated. On a failed save, the creature is frightened until the start of its next turn. If a creature's saving throw is successful, the creature is immune to Boxxy's Fear Aura for the next 24 hours.  A creature that is charmed by Boxxy automatically succeeds on its saving throw against this effect.  A creature is subjected to Boxxy's Pheromone Control trait (if active) before it is subjected to this trait.

Chaotic Disposition.  Once per turn, immediately after Boxxy casts a cantrip or spell, it rolls a d20. If it rolls a 1, it triggers a wild magic surge, the effect of which is determined by rolling percentile dice and consulting the Wild Magic Surge table in the “Sorcerer” section in chapter 3 of the Player’s Handbook.

If the Wild Magic Surge effect is a spell, it cannot be affected or enhanced by any of Boxxy's traits, and if it normally requires concentration, it doesn’t require concentration in this case; the spell lasts for its full duration.

Colossus Slayer (1/Turn). When Boxxy hits a creature with a weapon attack, the creature takes an extra 4 (1d8) damage if it’s below its hit point maximum.

Crystallize Magic.  When Boxxy casts an area spell, it can choose to create and store the spell in a spell gem, which lasts for 30 minutes before disappearing.  The spell is stored in the gem instead of having any effect.  A spell gem created by this trait can be thrown at a point up to 60 feet away as an action, shattering on impact and casting the stored area spell using Boxxy's Spellcasting DC centered on that point.

Death Strike. When Boxxy hits a creature that is surprised, the creature must make a DC 24 Constitution saving throw. On a failed save, the attack's damage is doubled.

Elusive.  No attack roll has advantage against Boxxy while it isn’t incapacitated.

Essence Concealment. Boxxy is immune to any effect that would sense its emotions or read its thoughts, divination spells, or any effect that magically reveal any information regarding its identity.

Evasion. When Boxxy is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, it instead take no damage if it succeeds on the saving throw, and only half damage if it fails.

False Appearance. While Boxxy polymorphed, it is indistinguishable from an ordinary example of what it is mimicking.

Favored Enemies.  Boxxy has advantage on Wisdom (Survival) checks to track Beasts, Humanoids, and Monstrosities, as well as on Intelligence checks to recall information about them.

Foe Slayer.  Boxxy can add its Wisdom modifier to the attack roll or the damage roll of an attack it makes against Humanoids.  Boxxy can choose to use this feature before or after the roll, but before any effects of the roll are applied.

Innate Spellcasting. Boxxy’s innate spellcasting ability is Constitution (spell save DC 27, +19 to hit with spell attacks). It does not need to concentrate on concentration spells, and can innately cast the following spells, requiring no material components:

At will: acid splash (17th level, 4d6 acid damage), entangle, jump, speak with plants, thorn whip (17th level, 4d6 piercing damage), vicious mockery (17th level, 4d4 psychic damage)

3/day each: counterspell (5th-level spell), dominate person (7th-level spell, 1 hour), enervation, enhance ability, mirror image*, shadow of moil, soul cage, web, wrath of nature

1/day each: dragon's breath (9th-level spell, 10d6 fire damage), flesh to stone, freezing sphere (9th-level, 13d6 cold damage), nondetection, plant growth, primordial ward, transport via plants,

*When Boxxy casts mirror image, each duplicate is a simulacrum of itself with 50 hit points which vanishes when reduced to 0 hit points, after 1 minute has passed, or Boxxy dismisses it.  Boxxy can issue orders to these duplicates telepathically.  It can't cast mirror image with this trait again until all three simulacrum have disappeared.

Ritual Casting:  Boxxy can cast a spell it knows as a ritual if that spell has the ritual tag without expending a spell slot or one of its uses per day.

Spellcasting. Boxxy is a 20th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 25, +17 to hit with spell attacks). Boxxy can cast shield and misty step at will, does not need to concentrate on concentration spells, and knows the following spells:

Cantrips (at will):  eldritch blast, fire bolt, frostbite, gust, lightning lure, mage hand, message, mold earth, ray of frost, shape water, shocking grasp, thunderclap, true strike

1st level (4 slots): armor of agathys, burning hands, ensnaring strike, expeditious retreat, hail of thorns, hex, hunter's mark, ice knife, longstrider, mage armor, magic missile, searing smite, thunderwave, 

2nd level (3 slots): Aganazzar’s scorcher, blur, cloud of daggers, cordon of arrows, enhance ability, flame blade, gust of wind, locate creature, locate animals or plants, magic weapon, mind spike, pass without trace, shadow blade, silence, spike growth

3rd level (3 slots): animate dead, call lightning, conjure barrage, darkness, dispel magic, elemental weapon, fear, flame arrows, fly, glyph of warding, haste, lightning arrow, lightning bolt, summon lesser demons, vampiric touch, water walk, wind wall

4th level (3 slots): black tentacles, blight, confusion, fire shield, freedom of movement, grasping vine, ice storm, summon greater demon

5th level (3 slots): animate objects, conjure volley, contact other plane, contagion, danse macabre, destructive wave, dominate person, immolation, infernal calling, planar binding, steel wind strike, swift quiver

6th level (2 slots): arcane gate, blade barrier, bones of the earth, chain lightning, circle of death, contingency, create undead, disintegrate, harm, instant summons, Tenser's transformation, wall of thorns

7th level (2 slots): delayed blast fireball, Mordenkainen's sword, reverse gravity, symbol, teleport, whirlwind

8th level (1 slot): Abi-Dalzim’s horrid wilting, antimagic field, antipathy/sympathy, maddening darkness, mind blank, power word stun, 

9th level (1 slot): gate, psychic scream, time stop,weird

* Boxxy casts the summon greater demon spell up to three times before combat; once as a 4th level spell to summon a [Tooltip Not Found] named Xera, once as an 8th level spell to summon a glabrezu named Kora, and/or once as a 4th level spell to summon a mezzoloth named Drea.  All three fiends willingly serve Boxxy, and choose to fail their Charisma saving throw against the spell.  Boxxy can issue its commands to these fiends telepathically instead of verbally.

Land's Stride.  Boxxy ignores nonmagical difficult terrain and has advantage on saving throws against plants that are magically created or manipulated to impede movement, such those created by the entangle spell.

Legendary Resistance (3/Day). If Boxxy fails a saving throw, it can choose to succeed instead.

Magic Locator Gland.  Boxxy generates a magical perception field in a 30-foot radius sphere centered on itself.  It can detect anything within the field as though it has blindsight and truesight and is under the effects of the detect magic spell.  The field can see through solid objects and magical darkness, and continues to function even if Boxxy is otherwise blinded.  This trait does not function in an antimagic field and ceases to function for 1 minute if Boxxy is subjected to a dispel magic spell.

Pheromone Control. Boxxy starts or stops exuding soothing pheromones at will.  While it is exuding pheromones, any humanoid that starts its turn within 20 feet of Boxxy must make a DC 27 Wisdom saving throw, unless Boxxy is incapacitated.  If Boxxy is currently fighting the creature or the creature is frightened of Boxxy, it makes its saving throw with advantage.  On a failed save, the creature is charmed until Boxxy or its allies do anything harmful to it or its allies.  If the effect ends on a creature, it becomes immune to Boxxy's Pheromone Control.  A creature is subjected to this trait before it is subjected to Boxxy's Butcher of Humanity trait.

Power Overwhelming (Overchannel). When Boxxy casts a spell of 1st through 5th level that deals damage, it can deal maximum damage with that spell.  The first time it does so, it suffers no adverse effect. If it uses this trait again before it finishes a long rest, it takes 2d12 necrotic damage for each level of the spell, immediately after it casts it. Each time it uses this feature again before finishing a long rest, the necrotic damage per spell level increases by 1d12. This damage ignores resistance and immunity.

Regeneration. Boxxy regains 10 hit points and 1 sorcery point at the start of its turn if it has at least 1 hit point. If Boxxy takes lightning damage, this trait doesn't function at the start of Boxxy's next turn.  If Boxxy is in sunlight, the amount of hit points and sorcery points it regains at the start of its turn is doubled.

Shapechanger. Boxxy can use its action to polymorph into an object, a Small, Medium, or Large creature (or its pseudopods into any body part thereof) it has seen, or back into its true chest-shaped form.  Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.  If part of Boxxy is severely damage, for example: being cut off, it shapechanges to grow a replacement; doing so restores the use of the damaged part, but does not restore any hit points.

Sneak Attack (1/turn). Boxxy deals an extra 35 (10d6) damage when it hits a target with a weapon attack and has advantage on the attack roll, or when the target is within 5 feet of an ally of Boxxy that isn’t incapacitated and Boxxy doesn’t have disadvantage on the attack roll.

Sorcery Points. Boxxy has 20 sorcery points and can never have more than this amount. Boxxy regains all spent sorcery points when it finishes a long rest.  Boxxy can transform unexpended sorcery points into one spell slot as a bonus action.  Any spell slot Boxxy creates with this feature vanishes when it finishes a long rest.  Alternatively, Boxxy can spend half as many sorcery points to regain the use of one expended spell slot.

• 1st level = 2 sorcery points
• 2nd level = 4 sorcery points
• 3rd level = 6 sorcery points
• 4th level = 8 sorcery points
• 5th level = 10 sorcery points
• 6th level = 12 sorcery points
• 7th level = 14 sorcery points
• 8th level = 16 sorcery points
• 9th level = 18 sorcery points

Metamagic (1/Turn).  When Boxxy casts a spell, it can spend sorcery points one one of the following Metamagic options:

• Quickened Spell.  When Boxxy casts a spell that has a casting time of 1 action, it can spend 2 sorcery points to change the casting time to 1 bonus action for this casting.
• Twinned Spell. When Boxxy casts a spell that can only target one creature and doesn’t have a range of self, it can spend a number of sorcery points equal to the spell’s level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip).  A spell capable of hitting more than 1 target such as eldritch blast or magic missile is ineligible for this option.

Spider Climb. Boxxy can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Storage. Boxxy has access to a demiplane.  The door to the demiplane does not require a flat surface, forming a circular portal in midair, which Boxxy can open or close at-will, requiring no action.  When using this trait to access its demiplane, it connects to same previously created demiplane, and cannot create a new one.  Attacks and spells can't cross through the entrance into or out of the demiplane, and creatures and objects cannot enter by any means unless allowed by Boxxy.

The walls to Boxxy's demiplane are immune to poison and psychic damage, resist all other types of damage, have an AC of of 17, and automatically fail all saving throws.  If a creature trapped inside the demiplane inflicts damage to the walls, all trapped creatures are ejected from the demiplane and appear in unoccupied spaces within 5 feet of Boxxy.  Boxxy takes any damage dealt to the walls of its demiplane.

Multiattack. Boxxy makes a different multiattack based on its current form.

• Doppelganger Form. Boxxy makes four weapon attacks, only one of which can be a grenade attack.  Alternatively, it executes the multiattack of one of its alternate forms. 
• Keira Form. Boxxy makes a longbow attack against any number of creatures within 10 feet of a point it can see within range of the weapon, or makes a rapier attack against any number of creatures within 5 feet of it.  Alternatively, Boxxy makes two weapon attacks choosing from any of the following weapons: dagger, longbow, or rapier.  It can substitute one dagger attack with its grenade.
• Mimic Form. Boxxy makes a one-handed longsword attack against any number of creatures within 5 feet of it or three two-handed longsword attacks.  It can substitute any longsword attack with its bite, dagger, or pseudopod.  It can substitute one longsword attack with its grenade.
• Sandman Form. Boxxy makes three skull staff attacks.  Alternatively, it makes one skull staff attack and casts a spell.  It can substitute any skull staff attack with its dagger or pseudopod.  It can substitute one of its skull staff attacks with a cantrip, and/or one of its skull staff attacks with its grenade.

Pseudopod (Any Form but Keira). Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 11 (1d8 + 7) bludgeoning damage.  If the target Large or smaller, it is grappled (escape DC 24). Until this grapple ends, the target is restrained.  Additionally, the target must succeed on a DC 24 Strength saving throw.  On a failed save, Boxxy can pull the target 5 feet towards itself.

Bite (Doppelganger or Mimic Form Only). Melee Weapon Attack: +16 to hit, reach 5 ft., one creature. Hit: 12 (1d10 + 7) piercing damage. If the target is Large or smaller, it is grappled (escape DC 24). Until this grapple ends, the target is restrained, Boxxy can automatically hit the target with its bite, and Boxxy can't make bite attacks against other targets.

Dagger. Melee or Ranged Weapon Attack: +16 to hit, reach 5 ft. or range 20/60 ft., one creature. Hit: 9 (1d4 + 7) piercing damage.

Grenade. Ranged Weapon Attack.  Boxxy throws a grenade at a point up to 60 feet away. Boxxy can throw either of the following grenades:

• Flashbang Grenade.  Each creature within 20 feet of the grenade must make a DC 15 Constitution saving throw.  On a failed save, a target is blinded, and deafened for 1 minute. If the saving throw fails by 5 or more, the target is stunned for the same duration.  At the end of each of its turns, the target can repeat the Constitution saving throw, ending all these effects on a success.
• Fragmentation Grenade.  Each creature within 20 feet of the grenade must make a DC 15 Dexterity saving throw, taking 5d6 piercing damage on a failed save, or half as much damage on a successful one. 
• Smoke Grenade.  One round after a smoke grenade lands, it emits a cloud of smoke that creates a heavily obscured area in a 20-foot radius. A moderate wind (at least 10 miles per hour) disperses the smoke in 4 rounds; a strong wind (20 or more miles per hour) disperses it in 1 round.
• Spell Grenade.  Boxxy throws a spell gem it has created with its Crystallize Magic trait.

Rapier (Doppelganger or Keira Form Only). Melee Weapon Attack: +16 to hit, reach 5 ft., one target. Hit: 11 (1d8 + 7) piercing damage.

Longbow (Doppelganger or Keira Form Only). Ranged Weapon Attack: +16 to hit, range 150/600 ft., one target. Hit: 11 (1d8 + 7) piercing damage, and the target’s speed is reduced by 10 feet until the end of its next turn.

Longsword (Doppelganger or Mimic Form Only). Melee Weapon Attack: +16 to hit, reach 5 ft., one creature. Hit: 11 (1d8 + 7) slashing damage, or 12 (1d10 + 7) slashing damage if used with two hands to make a melee attack.

Skull Staff (Doppelganger or Sandman Form Only). Melee Weapon Attack: +16 to hit, reach 5 ft., one target. Hit: 14 (2d6 + 7) bludgeoning damage plus 7 (2d6) force damage.

Transfamiliar. As an action, Boxxy can choose one fiend under its control.  Boxxy and the fiend teleport, swapping places.  When Boxxy appears in the space previously occupied by the fiend, it is in its true form, any previous shapechange undone.

Cunning Action/Vanish.  Boxxy can take the Dash, Disengage, or Hide action as a bonus action.  If Boxxy uses its bonus action to Hide, it can’t be tracked by nonmagical means, unless it chooses to leave a trail.

Second Wind (1/Short Rest). As a bonus action, Boxxy regains 25 (1d10 + 20) hit points.

Eyes of the Dead God. As a bonus action, Boxxy calls upon a shadowy power and casts its gaze at one creature it can see.  It immediately knows the name and current hit points of that creature.

Hurl Through Hell (1/Long Rest).  When Boxxy hits a creature with an attack, the creature vanishes, reappearing in the space it previously occupied at the end of Boxxy's next turn. If the target is not a fiend, it takes 10d10 psychic damage when it reappears.

Vengeance (1/Long Rest).  When Boxxy hits with a melee weapon attack, it can deal additional radiant damage equal to the total damage it has taken since the end of its last turn.

Don Facade. Boxxy polymorphs into "Keira Morgana" (a female swiftstride shifter ranger with red hair, cat ears, and a tail), "the Sandman" (a male goliath warlock concealed by a cowl and heavy cloak), "the Mimic" (a chest-shaped mimic rogue with spider legs, an eye on its front side, and multiple tentacle-like pseudopods), or back into its true form (a doppelganger with yellow eyes and a maw that opens vertically, splitting its face). It reverts to its true form if it dies. Any equipment it is wearing or carrying is borne by the new form or immediately stored or swapped with equipment in its Storage (Boxxy's choice).  Boxxy's ability to polymorph in nonmagical.

Stand Against the Tide.  When a hostile creature misses Boxxy with a melee attack, it can force that creature to repeat the same attack against another creature (other than itself) of Boxxy's choice.

Tomb of Levistus (1/Short Rest). When Boxxy take damage, it can entomb itself in ice, which melts away at the end of its next turn. It gains 200 temporary hit points, which take as much of the triggering damage as possible. Immediately after it takes the damage, it gains vulnerability to fire damage, its speed is reduced to 0, and it is incapacitated. These effects, including any remaining temporary hit points, all end when the ice melts.

Uncanny Dodge.  When an attacker that Boxxy can see hits it with an attack, it halves the attack’s damage against it.

Boxxy 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. Boxxy regains spent legendary actions at the start of its turn.

At-Will Spell.  Boxxy casts one of its at-will spells.

Bonus Action.  Boxxy uses one of its abilities or traits it can perform as a bonus action.

Cast a Spell (Costs 3 Actions). Boxxy casts a spell it knows with a casting time of 1 action, using a spell slot or use per day as normal.

Weapon Attack.  Boxxy makes one weapon attack.