As on all the lower planes, the River Styx flows through the top layer of Acheron, called Avalas. The Styx flows on many of Avalas's cubes--welling up from a crater on one cube to flow many miles, then leaking down into another crater, and reappearing on another cube. Sometimes the river takes a new course over a cube face, which can result in entire cities being washed away in a tide of forgetfulness and death.
Portals to other planes are fairly common. Usually, such gates appear in the mouths of the many tunnels that riddle most of Acheron's cubes.
OK, for starters...

Acheron is far different nowadays than described here. Hades actually makes better sense based on their description. Or we can simply state they are found anywhere along the River Styx.
For ability scores, Int is listed as "very high", which I'm assuming should be "very to high", meaning an Int in the 11-14 range.
Here are the ability scores of some other 14 HD fiends:
Nalfeshnee (H): Str 25, Dex 13, Con 27, Int 22, Wis 22, Cha 20
Nycaloth (L): Str 20, Dex 14, Con 25, Int 13, Wis 10, Cha 16
Gelugon (L): Str 23, Dex 21, Con 23, Int 22, Wis 22, Cha 20
So maybe...
Str 20, Dex 21, Con 25, Int 13, Wis 10, Cha 16?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.