What I want from a Monster Manual is fluff, ecology, hooks not just tables. I'm paying for the book so I want it inside as much as you want powers.
You mean like this?
Aboleths are hulking, amphibious creatures that hail from the Far Realm, a distant and unfathomable plane. They live in the Underdark, swimming through drowned crannies or creeping through lightless tunnels and leaving trails of slimy mucus in their wake. Malevolent and vile, aboleths bend humanoid creatures to their will, and more powerful aboleths can transform their minions into slimy horrors.
Aboleths lair in the deepest reaches of the Underdark, having slipped into the world from the Far Realm. However, lone aboleths can be found closer to the world's surface, haunting ruins, deep lakes, and old temples without hope or want of companionship. In many of these places, kuo-toa serve them.
Aboleths communicate via telepathy. They can speak and understand Deep Speech.
Sometimes aboleths live together as a brood or even in a collection of broods. Aboleth overseers also populate their lairs with humanoids that they've enslaved and transformed into slimy minions.
Or would you rather this:
The aboletth is a revolting fishlike amphibian found primarily in subterranean lakes and rivers. It despises all nonaquative creatures and attempts to destroy them on sight.
An aboleth has a pink belly. Four pulsating blue-black orifices line the bottom of its body and secrete gray slime that smells like rancid grease. It uses its tail for propulsion in the water and drags itself along with its tentacles on land. An aboleth weighs about 6,500 pounds.
Aboleths are cruel and highly intelligent, making them dangerous predators. They know many ancient and terrible secrets, for they inherit their parents' knowledge at birth and assimilate the memories of all they consume.
Aboleths are smart enough to refrain from immediately attacking land dwellers who draw near. Instead they hang back, hoping their prey will enter the water, which they often make appear cool, clear, and refreshing with their powers of illusion. Aboleths also use their psionic abilities to enslave individuals for use against their own companions.
Aboleths have both male and female reproductive organs. They breed in solitude, laying 1d3 eggs every five years. These eggs grow for another five years before hatching into full-grown aboleths. Although the young are physically mature, they remain with their parent for some ten years, obeying the older creature utterly.
Aboleths speak their own language, as well as Undercommon and Aquan.
I personally don't see how they are all that much different.
