Large Aberration, Chaotic Evil

Armor Class: 19 (Natural Armor)

Hit Points: 237 (25d10+100)

Speed: 0 ft., fly 40 ft. (hover)

STR 16/+3

DEX 18/+4

CON 19/+4

INT 22/+6

WIS 18/+4

CHA 20/+5

Saving Throws:, Constitution +11, Intelligence +13, Wisdom +11, Charisma +12
Damage Resistances: Cold, Fire, Force
Damage Immunities: Piercing, Slashing and Bludgeoning from Nonmagical Attacks, Psychic, Poison, Necrotic

Condition Immunities: Blinded, Charmed, Deafened, Exhaustion, Frightened, Petrified, Poisoned, Prone

Senses: Truesight 120 ft, Passive Perception 21

Languages: All Languages, Telepathy 300 ft.

Challenge: 22

Proficiency Bonus: +7

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

Reality Bend. The Gatekeeper emanates an otherworldly aura that distorts the surrounding reality. 

• In a 60 feet radius around the Gatekeeper the terrain is transformed into difficult terrain for creatures that are not aberrations.
• Each creature that starts their turn within 15 feet of the Gatekeeper must make a DC 22 Wisdom saving throw, on a failure, the Gatekeeper can teleport them anywhere within 60 feet of it and can also make them Frightened of it until the end of their next turn. 
• At the start of each round, all creatures within 30 feet of the Gatekeeper (Including the Gatekeeper) gain the effects of the Mirror Image spell that last until the end of the round. 
• Due to how it twists time and space around itself, Gatekeeper cannot be hurt by effects created outside its distorted pocket of reality. Gatekeeper is immune to the effects and damage of all spells and attacks that were made or cast by creatures further than 60 feet from it. 

Dimension Step. Each time an attack misses Gatekeeper, it can teleport up to 10 feet away. 

Cosmic Banishment. As a bonus action the Gatekeeper can cast the Banishment spell (DC 22) at a single creature within 60 feet of it. Whilst a creature is under the effects of the spell, it takes 5d10 psychic damage at the end of each of its turns. 

• While the Gatekeeper is concentrating on the spell, it can use its bonus action again to make another creature within 60 feet make the saving throw, making them also suffer from the effects of the spell as well.
  • For each additional banished creature, Gatekeeper gains a -2 penalty on its concentration checks. 
  • At the end of each of their turns, before taking damage from the effect, a banished creature can choose to end the effect on themselves. If they do this however, they become charmed by the Gatekeeper and have to obey all of its telepathic commands. The creature stops being charmed only if they are incapacitated. While charmed in this way, the affected creature is considered an Aberration. 

Actions:

• Warp Beam: The Gatekeeper creates a beam of warp energy forming a line 60 feet long and 15 feet wide that tears apart and displaces particles of creatures and objects. Each creature in the area must make a DC 22 Dexterity saving throw Objects automatically fail on the saving throw. On a failure, they take 66 (12d10) force damage and are teleported for an amount of feet equal to the damage taken, appearing in the nearest unoccupied space. The affected creatures must also roll a d10 to determine the direction of their teleportation
  • 1 – North
  • 2 – North-East
  • 3 – East 
  • 4 – South-East
  • 5 – South
  • 6 – South-West 
  • 7 – West 
  • 8 – North-West
  • 9 – Up
  • 10 – Down 

On a success, the affected creatures only take half damage, and are not teleported. 

• Touch from the Other Side. Melee Spell Attack: +13 to hit, reach 5 ft., one target. Hit: 110 (20d10) force damage. If this brings a creature to 0 Hit Points, the creature becomes stabilized and immune to damage and their body is fragmented into 3 pieces, each of which the Gatekeeper can immediately teleport anywhere within 30 feet of it. The affected creature cannot regain hit points as long as its fragments are all further than 5 feet from each other.
  After 1 hour, if the creature has not recovered Hit Points and its parts are still scattered, the Aberration can use its action to transform it into one CR 8 or lower Aberration, two CR 4 or Lower Aberrations, or three CR 2 or lower Aberrations.
  • However the cumulative CR of the Aberrations cannot exceed the CR of the original creature, or half of its Character Level. 
  • This attack cannot be used to kill a creature.
• Diluvian Gateway.  The Gatekeeper conjures one aberration of CR 3 or lower that shares its initiative and plays either directly before or after the Gatekeeper.

Legendary Actions (2x):

• Diluvian Gateway (Costs 2 Actions). The Gatekeeper conjures one aberration of CR 3 or lower that shares its initiative and plays either directly before or after the Gatekeeper. 
• Vision of Beyond. A creature within 120 feet of the Gatekeeper must make a DC 15 Wisdom saving throw. On a failed saving throw, they become blinded and deafened while not within 30 feet of the Gatekeeper.
  While affected by this feature, they see themselves in a strange cosmic void, and the only other thing they can see is a large gate that corresponds with the nearest point within 30 feet of the Gatekeeper.
  The affected creature can repeat the saving throw at the end of each of their turns.
• Weight of the Cosmos. A creature within 60 feet of the Gatekeeper becomes encumbered by gravity. They must make a DC 15 Strength saving throw. On a failure, they take  3d10 force damage, their movement speed is halved, and they subtract 1d8 from each saving throw, ability check and attack roll until the end of their next turn. On a success, the damage is halved, and they don’t suffer from any additional effects. 

Reactions:

• Phase Shift. Upon taking damage, the Gatekeeper can swap its place with an aberration within 120 feet of it.

Holder of Keys. When a creature within 60 feet of the Gatekeeper casts a spell, it can make an Intelligence Check contested by the creature’s spellcasting Ability Check. If the Gatekeeper succeed in the contest, it can change the spell’s target and also make the original caster unable to willingly break concentration on the spell or cast another concentration spell while they are concentrating on the original spell.