Gargantuan elemental, unaligned
Armor Class 20 (natural armor)
Hit Points 145 (10d20 + 40)
Speed 0 ft., swim 50 ft.
Saving Throws Dex +17, Cha +11
Damage Vulnerabilities lightning
Damage Resistances cold, fire, thunder; bludgeoning, piercing, and slashing from nonmagical attacks
Damage Immunities poison
Condition Immunities exhaustion, paralyzed, petrified, poisoned, stunned
Senses darkvision 60 ft., passive Perception 10
Challenge 22 (41,000 XP)
Wave-Maker. As a bonus action after moving at least 30 feet in water, the akaei can send a tsunami through the water around it in a 120-foot-radius circle centered on itself. A wall of water forms from the akaei. This wall is 300 feet long, 300 feet high, and 50 feet thick. The wall lasts for 1 minute.
When the wall appears, each creature within the area of the tsunami must make a DC 25 Strength saving throw. On a failed save, a creature takes 100 bludgeoning damage.
At the start of each of the akaei's turns after the wall appears, the wall, along with any creatures in it, moves 50 feet away from it. Any Huge or smaller creature inside the wall or whose space the wall enters when it moves must succeed on a Strength saving throw or take 17 (5d6) bludgeoning damage and be pushed 100 feet under by the wave current. A creature can take this damage only once per round. At the end of the akaei's turn, the wall's height is reduced by 50 feet, and the damage creatures take from the wave on subsequent rounds is reduced by 1d10. When the wall reaches 0 feet in height, the wave subsides.
A creature caught in the wall can move by swimming. Because of the force of the wave, though, the creature must make a successful DC 20 Strength (Athletics) check in order to move at all. If it fails the check, it can't move. A creature that moves out of the area falls to the ground.
Legendary Resistance (3/Day). If the akaei fails a saving throw, it can choose to succeed instead.
Magic Weapons. The akaei's weapon attacks are magical.
Siege Monster. The akaei deals double damage to objects and structures (included in Wave-Maker).
Multiattack. The akaei makes two attacks with its tail.
Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 28 (4d8 + 10) bludgeoning damage.
Engulf. The akaei moves up to its speed. While doing so, it can enter Huge or smaller creatures' spaces. When the akaei enters a creature's space using engulf, the creature must make a DC 25 Dexterity saving throw.
On a successful save, the creature can choose to be pushed 5 feet back or to the side of the akaei. A creature that chooses not to be pushed suffers the consequences of a failed saving throw.
On a failed save, the target is swallowed. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the akaei, and it takes 56 (16d6) acid damage at the start of each of the akaei's turns.
If the akaei takes 60 damage or more on a single turn from a creature inside it, the akaei must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the akaei. If the akaei dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.
Spew Debris (Recharge 5-6). The akaei exhales sandy debris in a 90-foot cube. Each creature in that area must make a DC 25 Dexterity saving throw. A creature takes 33 (6d10) bludgeoning damage on a failed save, or half as much damage on a successful one. A creature that fails the save by 5 or more is knocked prone.
A legendary red manta ray the size of an island, the akaei is an enigmatic creature that swims the unplumbed depths of Grisaire. It is considered something like a primordial creature, created at the earliest times by the gods as one of the Old Ones. It is worshiped as a great spirit of nature by many cultures, particularly in Lozor. It is said to have spawned a myriad of creatures from the nutritious red sand encrusted on its body, including the race of jinei.