Large Monstrosity, Unaligned
Armor Class: 18 (Natural Armor)

Hit Points: 161 (19d10+57)

Speed: 30 ft.

STR 16/+3

DEX 20/+5

CON 16/+3

INT 10/+0

WIS 14/+2

CHA 10/+0

Saving Throws: Constitution +7, Wisdom +6

Damage Resistances: Acid, Bludgeoning, Psychic, Piercing and Slashing from nonmagical attacks

Damage Immunities: Cold (Special), Poison

Condition Immunities: Blinded, Poisoned

Skills: Athletics +7, Acrobatics +9, Perception +6

Senses: Blindsight 60 ft., Passive Perception 16

Languages: Understands Common, but can’t speak. 

Challenge: 11

Proficiency Bonus: +4

Quicksilver Form. Can move through space as narrow as 1 inch without squeezing. Beast of Thousand Forms also cannot have its form altered by any spells or effects against its will. 

Limited Heat Tolerance. if Beast of Thousand Forms would receive 15 or less Fire Damage from an effect, it takes no fire damage from the effect instead. But if it receives 30 or more Fire Damage from an effect, that damage is increased by 10.

Freezing Point. While Beast of Thousand Forms is immune to Cold damage, it can still hinder its movement and shapeshifting. If the Beast of Thousand Forms were to take 20 or more Cold damage since the end of its last turn, its movement speed is halved and it loses its ability to shapeshift until the end of its next turn. 

If it were to take 50 or more Cold Damage since the end of its last turn, it is petrified until the end of its next turn.
This effect and all accumulated Cold damage is lost if Beast of Thousand Forms takes any Fire damage. 

Killer’s Disguise. As an action, Beast of Thousand Forms can assume the shape of any creature or object it has seen of size small, medium or large, becoming indistinguishable from the original. It retains its statistics, but cannot use any of its actions or reactions in this form. 

Mercurial Killer. Beast of Thousand Forms is an artificially created monster designed to be a perfect killing machine, capable of changing its form to best exploit the weaknesses of its adversaries. As a bonus action, it can shapeshift into one of its available forms, giving it the following actions and properties:

Savage Slasher. Beast of Thousand Forms transforms into a bestial centipede-like monster with about half a dozen razor-sharp appendages. Trading all of its defence to focus all of its offensive capability on a single creature. 

• When Beast of Thousand Forms shapeshifts into this form, it can immediately make 2 Savage Slashes
• All attacks against the Savage Slasher form are made with advantage. 
• Savage Slasher makes 2 Savage Slash attacks as part of its Attack of Opportunity and it can make an Attack of Opportunity once on every creature’s turn without expending a reaction, but it can’t be used on the same turn as a normal reaction.
  • Creatures provoke Attacks of Opportunity from Savage Slasher even if they took the Disengage action. 
• Actions
  • Multiattack. Beast of Thousand Forms makes 4 Savage Slash attacks against a single creature. 
  • Savage Slash. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 14(2d8+5) slashing damage.

Quicksilver Duelist. Beast of Thousand Forms transforms into a thin humanoid looking form with elongated limbs and assuming a fencing stance. 

• If Beast of Thousand Forms shapeshifts into this form using a bonus action, it can immediately use Riposte Stance without spending an action.
• Beast of a Thousand Forms can shapeshift into this form as a reaction when missed by a melee attack, immediately using the Extended Riposte as part of the reaction.
• Actions.
  • Multiattack. Quicksilver Duelist uses two Quicksilver Thrust attacks
  • Quicksilver Thrust. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 14(2d8+5) piercing damage.
  • Extended Thrust. Quicksilver Duelists turns its limb into a sharp and thin blade and thrusts it in a 40 ft. long and 5 ft. wide line. All creatures caught in the area must make a DC 17 Dexterity saving throw, taking 18(3d8+5) piercing damage on a failure.
  • Riposte Stance. Quicksilver Duelist’s DC is increased by +10 against the next melee attack made against it until the start of its next turn. 
• Reactions.
  • Extended Riposte. When missed by a melee attack, Quicksilver Duelist can move anywhere within 5 ft. of the attacker without triggering attacks of opportunity and make an Extended Thrust. The attacker automatically fails on the saving throw and takes extra 1d8 piercing damage. 

Winged Doom. Beast of Thousand Forms transforms into a quick and elusive bat-like form with massive wings and enormous grasping talons. 

• When Beast of Thousand Forms shapeshifts into this form, it can immediately use Disengage or make one Talon Attack against a creature within reach without expending an action.
• Winged Beast can use Disengage as a bonus action
• In this form, Beast of Thousand Forms gains 80 ft. of flying speed. 
• Creatures grappled by Winged Doom are also restrained and they take 14(2d8+5) piercing damage at the start of each of their turns. 
• Talon Dive. If Winged Doom moves at least 50 ft. in a straight line towards a creature and hits it with a Talon attack. The attack deals extra 9(2d8) piercing damage, and Winged Doom  gains extra 50 ft. of flying speed until the end of its turn.
  • Actions. 
    • Multiattack. Winged Doom makes two Talon attacks
    • Talon. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 14(2d8+5) slashing damage and the target is grappled (Escape DC 15). This attack is an automatic hit against grappled creatures. 

Axe Whirlwind. Beast of Thousand Forms transforms its upper torso into a giant elongated axe and begins to quickly rotate, creating a deadly vortex. 

• When Beast of Thousand Forms shapeshifts into this form, it can make a Slashing Whirlwind attack. 
• Axe Whirlwind’s movement speed is halved. 
• As long as the Axe Whirlwind is not incapacitated, any creature ending their turn within 20 ft. of Axe Whirlwind that is not prone or at least 15 ft. above it must make a DC 15 Dexterity saving throw, taking 14(2d8+5) Slashing damage on a failure.
  • Actions.
    • Slashing Whirlwind. All creatures within 20 ft. of the Axe Whirlwind must make a DC 15 Dexterity saving throw, taking 14(2d8+5) slashing damage on a failure, or half as much on a success. 
    • Giant Chop. Melee Weapon Attack: +9 to hit, reach 20 ft., one target. Hit: 32 (6d8+5) Slashing Damage