Aqulia, Decimator, Karma of Daythunder, Eye of Twilight

Helium Flash / Thundercloud / Black Tide Sync. The Decimator uses three separate escalating counters. Each round, it gains 1 stack of each (up to 20). Stacks can be spent by abilities for amplified effects. Some effects reduce these stacks.

Hundred Eyes. Damage dealt to its constructs (Daythunder Raven, Shoot of Hundred Eyes, Twig of Hundred Eyes, Languid Ethmoid Bone, Dried Lacrimal Bone) is also dealt to the Decimator. Killing blows on those constructs deal 40 force damage to the Decimator and cause the constructs to become untargetable while regenerating.

Tides Below. Every time the Decimator or the Black Tide acts, increase Black Tide Sync Rate by 1. This causes its attacks to deal an additional 2d10 necrotic damage per stack. At the end of each creature's turn, if that creature attacked, it takes 2d10 true damage per stack. Reducing either bone to 0 HP reduces the Sync Rate by 3.

Black Tide. At initiative 10, the Black Tide acts, inflicting 1 stack of Rot (see Rot below) on all creatures. If all living creatures are affected by Tide-Corrosion or dead, the Decimator wins automatically.

Rot. A stacking condition. Each stack deals 1d10 necrotic damage per turn and reduces healing by 5 per stack. 10 stacks: the creature gains Tide-Corrosion, halving all resistances and doubling damage from Decimator.

Solar Storm. While Helium Flash is above 5, all enemies begin their turn taking 4d10 fire damage.

Stormfall. While Thundercloud is active, all enemies begin their turn taking 4d10 lightning damage.

Phase Shifts.
- Phase 1: Uses Fire abilities and Helium Flash.
- Phase 2 (below 1060 HP): Uses Lightning abilities and Thundercloud.
- Phase 3 (below 530 HP): Uses Imaginary damage and Black Tide Sync.

Multiattack. Makes 3 attacks or uses one major action.

Fury, Incineration of Dawn and Dusk (Recharge 5-6, Phase 1).
All creatures in 120 ft. must make a DC 25 Dex save or take 20d10 fire damage, divided evenly among all targets. Raises Helium Flash by 3. Restores Twig and Shoot of Hundred Eyes. 

Three Thousand Leagues Ablaze (Phase 1).
Makes 6 fire bolt attacks (+17 to hit, 4d10 fire each) from the left side of the battlefield. First strike on each creature is prioritized, remaining hit random targets. Increases Helium Flash by 2.

Flame Beyond the Horizon (Phase 1).
Deals 15d10 fire damage to all creatures. Increases Helium Flash by 2.

Exhalation of the Month of Everyday (Phase 1).
Deals 12d10 fire damage to all creatures and reduces their movement by half until end of their next turn. Increases Helium Flash by 2.

Wrath, Rend of Eternal Sky (Recharge 5-6, Phase 2).
Consumes up to 20 Thundercloud stacks. Deals 10d10 lightning damage to all targets and 1d10 lightning to a random target per stack consumed. Also deals 1d10 lightning to self per 2 stacks consumed.

Thunder From the Distance (Phase 2).
Makes 6 lightning bolt attacks (+17 to hit, 4d10 lightning each). First strike on each creature is prioritized. Increases Thundercloud by 5.

Surge Across the Leagues (Phase 2).
Deals 15d10 lightning damage to all targets. Increases Thundercloud by 5.

Illumination of the Month of Fortune (Phase 2).
Deals 12d10 Lightning damage to all creatures and reduces their movement by half until end of their next turn. Increases Thundercloud by 5. Also restores Twig and Shoot of Hundred Eyes.

Ashes to the Distant Shore (Phase 3).
Deals 100 force damage to one target and inflicts 3 stacks of Rot. Restores Languid Ethmoid Bone.

Unmaking Ashes: Godsfall (Recharge 5-6, Phase 3).
Deals 20d10 force damage to all targets, restores both Bones. Inflicts 2 stacks of Rot.

Extinguishment of the Savaged Star (Phase 3).
Deals 15d10 force damage, evenly distributed among all targets. Restores Dried Lacrimal Bone.

Legendary Titan. The Decimator can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. It regains spent legendary actions at the start of its turn.

Shoot of Hundred Eyes. Launches a burst of radiant light at a target that dealt damage last turn. That target must succeed a DC 25 Con save or be blinded until end of next turn and take 6d10 radiant damage.

Twig of Hundred Eyes. Targets a creature that cast a spell last turn. That creature must succeed a DC 25 Int save or take 6d10 psychic damage and have disadvantage on concentration checks until the end of its next turn.

Daythunder Raven (2x Max, Restores if Killed). Summons a raven (AC 18, 50 HP) that boosts Helium Flash (Phase 1) or Thunderclouds (Phase 2) by 5 per round. Killing it reduces the appropriate meter by 10.

Splendor, Like clouds cresting the sky. Charges for 1 round. Summons in two Daythunder ravens. On Next turn, casts Fury, Incineration of Dawn and Dusk as a free action.

Thunderclap, Quake of mount and seas. Charges for 1 round. Summons in two Daythunder ravens. On Next turn, casts Wrath, Rend of Eternal Sky as a free action.

Eye of Terror. Charges for 1 round. On next turn, casts Unmaking Ashes: Godsfall as a free action.

 The Dark Tides Cometh. Adds Black Tide to initiative. Black Tide sync begins stacking.

Tide Collapse. If Sync Rate exceeds 20, can cause a karmic implosion — all targets must make a DC 25 Constitution saving throw or be reduced to 0 HP. Half damage on success (10d10 necrotic).