Ancient Dragosuarus

Gargantuan Dragon Beast, Unaligned

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AC 22
HP 546 (28d20+252) 
Speed 30 ft, Swim 60 ft., Fly 10 ft. (Hover) 
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STR: 29 (9) INT: 12 (1)
DEX: 10 (0) WIS: 16 (3)
CON: 28 (9) CHA: 15 (2) 
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Saving Throws - Strength +17, Constitution +18, Wisdom +12
Skills - Athletics +17, Perception +11, Survival +11
Damage Immunities - Force, Poison
Condition Immunities - Charmed, Frightened, Poisoned 
Senses - Darkvision 120 ft., Tremorsense 60 ft.,  Passive Perception 13
Languages - Understands Primordial
Challenge - 29
Proficiency Bonus - +8

TRAITS

Amphibious - The Dragosaurus can breathe air and water.

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

Magic Resistance - The Dragosaurus has advantage on saving throws against spells and other magical effects.

Crystal Resonance - If the Dragosaurus were to take Force damage, it is supercharged by that damage instead, gaining a Resonance charge each time. These Charges can be spent to power abilities (listed below) or to add 1d12 Force damage per charge spent on a successful attack. 

ACTIONS

Multiattack - The Dragosaurus makes three Shredding Claw attacks. It can replace one attack with a use of its Toxic Tail.

Shredding Claw - Melee or Ranged Attack Roll +18, reach 5 ft., range 60ft. Hit: 35 (4d12+9) Slashing damage.

Toxic Tail - Melee Attack Roll +18, reach 15 ft. Hit: 15 (2d10+9) Piercing damage and 38 (7d10) Poison damage, and the target has the Poisoned condition. At the end of the target's next turn, it can make a DC 22 Constitution saving throw to end the condition.  

Crystal Beams (1 Resonance Charge) - Dexterity Saving Throw: DC 22, each creature in a 120-foot-long, 15-foot-wide Line. Failure: 77 (22d6) Force Damage and the creature is knocked Prone. Success: Half damage. 

After this attack, crushing force suffuses the area through which the beam traveled for 1 minute. Other creatures moving through this area must spend 10 ft. of Movement for every 5 ft. moved. 

Resonant Frequency - The Dragosaurus causes strange harmonic resonations in the crystals growing from its body, dealing 6 (2d10) Force damage to all creatures in a 5 ft. Radius centered on itself. This grants the Dragosaurusus 1 Resonance Charge.

BONUS ACTIONS

Crushing Singularity (3 Resonance Charges) - The Dragosaurusus creates a powerful gravitational 60 ft. Emanation centered on itself that lasts for 1 minute. All creatures within the Emanation have their speed reduced by 10 ft. and must make a DC22 Strength saving throw. Failure: 22 (4d10) Force Damage and the creature is pulled 30 ft. closer to the Dragosaurusus. If a creature ends its turn within 5 ft. of the Dragosaurusus, the damage is doubled. Success: Half damage and the creature is not moved. 

Anti-Gravity Stomp (3 Resonance Charges) - The Dragosaurusus creates a 60 ft. Emanation centered on itself where gravity becomes reversed for 1 minute. While this effect is active, the Dragosaurusus’s Fly speed is increased to 60 ft. All other creatures within the Emanation begin floating helplessly in the air, orbiting the Dragosaurus. To avoid this effect, a creature can make a DC22 Dexterity saving throw to grab onto a fixed object on the ground. 

LEGENDARY ACTIONS

Legendary Action Uses: 3. (4 in Lair). Immediately after another creature's turn, The Dragosaurus can expend a use to take one of the following actions. The Dragosaurus regains all expended uses at the start of each of its turns.

Pounce - The Dragosaurus moves up to half its Speed, and it makes one Shredding Claws attack. 

Gravitational Shift (3 Resonance Charges) - The Dragosaurus uses its Crushing Singularity or Anti-Gravity Stomp. The Dragosaurus cannot take this Action again until the start of its next turn. 

REGIONAL EFFECTS

The region containing an Ancient Dragosaurus’s lair is warped by its presence, creating the following effects. 

Newtonian Shift - Every 8 hours the gravity in the area shifts a bit, becoming heavier or lighter than normal. 

Heavier - Creatures are treated as 1 size smaller to determine their Carry Capacity and how much they can drag, lift, or push. Speed is reduced by 10ft. and Jumping height / distance is halved. The distance of Ranged weapon attacks are halved, but add an additional 1d10 Force damage. 

Lighter - Creatures are treated as 1 size larger to determine their Carry Capacity and how much they can drag, lift, or push. Speed is increased by 10ft. and Jumping height / distance is doubled. Ranged weapon attack damage is doubled.

Gravitational Anomalies - The area within 1 mile of the lair is affected by strange localized changes to gravity. For every hour of travel, a creature has a 1 in 5 chance of stumbling across one of these anomalies. Roll a d10. On a roll of 1, the creature encounters a Gravity Well. On a roll of 10, the creature encounters an Anti-Gravity Zone. 

These anomalies typically form in the shape of a sphere, with a radius of up to 50 ft.

Gravity Well - Creatures entering the Gravity Well or starting their turn within it must make a DC16 Strength Saving Throw. Failure: The creature is pulled 15 ft. toward the center of the Gravity Well.

While within the Gravity Well, your speed is doubled while moving toward the center, but halved when moving away from the center. A creature who moves within 10 ft. of the center of the Gravity Well or starts its turn there takes 4d10 Force damage.

Anti-Gravity Zone - Creatures entering the Anti-Gravity Zone immediately find themselves beginning to float off the ground. While floating in this way, you are unable to control your movements without some way of propelling yourself through the air (spells, pushing off of things, etc…). Each round you are within the zone, you move 15ft. upward. If this movement causes you to reach the top of the anomaly, you bob there harmlessly.