Before the coming of the gods, aboleths lurked in primordial oceans and underground lakes. They reached out with their minds and seized control of the burgeoning life-forms of the mortal realm, making those creatures their slaves. Their dominance made them like gods. Then the true gods appeared, smashing the aboleths’ empire and freeing their slaves.

Aboleths have never forgotten.

Eternal Memories. Aboleths have flawless memories. They pass on their knowledge and experience from generation to generation. Thus, the injury of their defeat by the gods remains perfectly preserved in their minds. Ancient Aboleths do not have better memories than their younger kin, nor do they remember necessarily more about the earliest days, but they have had more time to hone practical uses for their knowledge, drawing connections and seeing deeper meanings in events of the past, and to grow more cunning and malicious. 

Aboleths’ minds are treasure troves of ancient lore, recalling moments from prehistory with perfect clarity. They plot patiently and intricately across eons. Few creatures can conceive of the extent of an aboleth’s plan.

Gods in the Lake. Aboleths dwell in watery environments, including ocean abysses, deep lakes, and the Elemental Plane of Water. In these domains and the lands that adjoin them, aboleths are like gods, demanding worship and obedience from their subjects. When they consume other creatures, aboleths add the knowledge and experiences of their prey to their eternal memories. Aboleth ancients were there first, however, and most often have claimed the choicest, deepest, most well-defended spots, or those with the best access to slaves or other resources. These Aboleths are most commonly the Nobles of their ancient race. 

Aboleths use their telepathic powers to read the minds of creatures and know their desires. An aboleth uses this knowledge to gain a creature’s loyalty, promising to fulfill such wants in exchange for obedience. Within its lair, the aboleth can further use its powers to override senses, granting creatures, such as its followers, the illusion of promised rewards.

Enemies of the Gods. The aboleths’ fall from power is written in stark clarity on their flawless memories, for aboleths never truly die. If an aboleth’s body is destroyed, its spirit returns to the Elemental Plane of Water, where a new body coalesces for it over days or months. An ancient may have scars on its body left there by the gods themselves. Perhaps the aboleth ancient keeps the scars each time they reform as a badge of pride in having spat defiance in the face of the gods in person, or perhaps injuries left by a god are permanent, even after reforming a new body. Either way, ancient aboleths take pride in physical signs of their defiance of the gods who took everything from them and banished them to the dark.

Ultimately, aboleths dream of overthrowing the gods and regaining control of the world. Aboleths have had untold eons to plot and to prepare their plans for perfect execution.

Lair Actions
When fighting inside its lair, an aboleth ancient can invoke the ambient magic to take lair actions. On initiative count 20 (losing initiative ties), the aboleth ancient takes a lair action to cause one of the following effects:

The aboleth ancient casts phantasmal force (no components required) on any number of creatures it can see within 60 feet of it. While maintaining concentration on this effect, the aboleth ancient can’t take other lair actions. If a target succeeds on the saving throw or if the effect ends for it, the target is immune to the aboleth ancient’s phantasmal force lair action for the next 24 hours, although such a creature can choose to be affected.
Pools of water within 90 feet of the aboleth ancient surge outward in a grasping tide. Any creature on the ground within 20 feet of such a pool must succeed on a DC 16 Strength saving throw or be pulled up to 20 feet into the water and knocked prone. The aboleth ancient can’t use this lair action again until it has used a different one.
Water in the aboleth ancient’s lair magically becomes a conduit for the creature’s rage. The aboleth ancient can target any number of creatures it can see in such water within 90 feet of it. A target must succeed on a DC 16 Wisdom saving throw or take 16 (3d6+6) psychic damage. The aboleth ancient can’t use this lair action again until it has used a different one.

Regional Effects
The region containing an aboleth ancient’s lair is warped by the creature’s presence, which creates one or more of the following effects:

• Underground surfaces within 1 mile of the aboleth ancient’s lair are slimy and wet and are difficult terrain.
• Water sources within 1 mile of the lair are supernaturally fouled. Enemies of the aboleth ancient that drink such water vomit it within minutes.
• As an action, the aboleth ancient can create an illusory image of itself within 1 mile of the lair. The copy can appear at any location the aboleth ancient has seen before or in any location a creature charmed by the aboleth ancient can currently see. Once created, the image lasts for as long as the aboleth ancient maintains concentration, as if concentrating on a spell. Although the image is intangible, it looks, sounds, and can move like the aboleth ancient. The aboleth ancient can sense, speak, and use telepathy from the image’s position as if present at that position. If the image takes any damage, it disappears.

If the aboleth ancient dies, the first two effects fade over the course of 3d10 days.