Atheon, Time's Conflux

When legends and rumors of the Vault of Glass are spoken of, the mythical Vex Axis Mind known as Atheon is not far out of mind: a hyper-advanced machine said to have terrifying control over time itself.

Time's Conflux. Atheon's physical form resembles a Vex Minotaur, though much larger and glowing with the power of the Vault of Glass itself. Much like its more common counterparts, it wields a Torch Hammer that it uses to suppress and eradicate threats, but that is where the commonalities end. Atheon is said to sidestep time itself: in fact, it isn't clear whether Atheon created the Vault of Glass or was created by it. Somehow, multiple timestreams of the Vault converge onto this Vex Mind, an axis in the truest sense of the word.

Overseer of the Vault. Those who attempt to describe the ultimate goals of the Vex are often stymied by the machines' inscrutable nature and nearly-impossible abilities. The purpose of the Vault of Glass itself is unclear, and likely manifold. Those who have escaped its clutches speak of ontological weapons that can erase a being from time and memory; others recall traversing pathways of time until they left the Vault before they had even entered. Atheon, then, may be at the center of it all: an overseer for the time- and reality-bending experiments of the Vex carried out in pursuit of an unknown goal.

Atheon waits in the Vault of Glass, a stronghold of the Vex that exists both at the juncture of multiple timestreams and outside of normal time. It is a testing ground for the machines' experiments with reality-warping warfare, an immense supercomputer where the material universe bends to their algorithmic will. Inside the Vault, Atheon is god in the machine, a tailor fraying apart timestreams and using its will as a needle to thread the fates to its advantage.

Lair Actions

On initiative count 20 (losing initiative ties), Atheon takes a lair action to cause one of the following effects; Atheon can’t use the same effect two rounds in a row. The lair actions it can use also depend on whether the timegates can be opened or not.

Timegates Active

• Neutralization Protocol. Atheon uses Open Timestreams if at least one timegate is still active; otherwise, it uses Expunging Field.
  
  • Open Timestreams. Atheon opens a timegate, and two creatures farthest away from it are automatically chronoported to a different timestream of the Vault of Glass. It will always send creatures to the future if it can, otherwise it will send them to the past. It cannot use this lair action again until the transported creatures either die or return to the present. When both creatures return to the present by passing through the gate, that timegate can no longer be opened. Atheon can't use this lair action if both timegates are deactivated.
  • Expunging Field. A 10-foot radius sphere of shimmering energy surrounds one creature in Atheon's lair, following the creature as it moves. At the end of that creature's turn, the sphere solidifies into a barrier of glass, trapping any creatures in the area. Attacks and spells cannot cross the barrier. The barrier has an AC of 15 and 30 hit points. The barrier can only be destroyed from the outside: a single strike from the Fatesmith's Aegis breaks the barrier. If the barrier is not destroyed by the end of the target's next turn, all creatures inside of it take 55 (10d10) psychic damage and the barrier dissipates.
• Reinforcements. Atheon summons up to four Vex harpies in different spaces within 10 feet of itself. The summoned creatures act on their own turn in the initiative order. Only six summoned harpies can be active at any time. All harpies also die when Atheon dies.
• Radiolarian Accelerant. Atheon causes radiolarian fluid to burst from the ground underneath one creature in its lair, not including itself. The target must succeed on a DC 15 Constitution saving throw or become infected for 1 minute. Undead and constructs are not immune to this infection. An infected creature takes 16 (3d10) radiant damage at the start of each of its turns for 1 minute, and gains an additional action on its turn that it can use to make one attack, cast one cantrip, Dash, Disengage, Hide, or Use an Object. An affected creature may repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. This effect also ends when an affected creature enters the Cleansing Field of the Fatesmith's Aegis.

Combat in the Vault of Glass

Atheon follows a specific set of tactics when it is engaged in the Vault of Glass.

Phase 1: Eschaton Throne

The first measure Atheon takes to deal with intruders to the Vault is to transport them to a different timestream. In the first round when combat starts, Atheon always uses its Open Timestreams lair action to transport two creatures, and the Fatesmith's Aegis, to the distant future. The distant future is controlled by an Eschaton Oracle and contains 8 Vex goblins and 4 Vex hobgoblins. The Eschaton Oracle sings its Void Song, and can use its knowledge of the past to force creatures to reroll attack rolls, saving throws, and ability checks. The Oracle must be destroyed in order to empower the Fatesmith's Aegis, and for the transported creatures to return to the present.

Phase 2: Primeval Throne

If the transported creatures escape the distant future, Atheon then transports two different creatures and the Fatesmith's Aegis to the distant past. The distant past is controlled by a Primeval Oracle and contains one tyrannosaurus rex and six pteranodons. The Primeval Oracle sings its Void Song, while also empowering the non-Vex creatures with Radiolarian Accelerant. The Oracle must be destroyed in order to empower the Fatesmith's Aegis, and for the transported creatures to return to the present.

Phase 3: Fall of Atheon

Once the timegates are deactivated, Atheon summons an Imminent Oracle and begins to engage the party more ferociously. The Imminent Oracle must be destroyed in order to empower the Fatesmith's Aegis. Using the special attack of the Aegis causes Atheon to lose its Deterministic Armor, making it vulnerable to attack.