Aboleth Take Over the World

[The Forsaken One]

Planar Bleeds actually really do exist. (MotP)

And there is a city which continually shifts from plane to plane through major planar bleeds which the ruler of the city is able to create himself.

So I don't know what kinda cosmology you use but that might provide an interesting quest if your PC's are evil to gain that information to flood the world or melt the caps through some or maybe even just one major planar bleed.

If your PC's are high enough level and you use a multiverse as cosmology you might just send them on an interplaner quest and chase to prevent the Aboleth and their evil minions and thralls from aquiring this information from the ruler of the city and through a wild planar goose chace they might finally catch up with the city with means of some good sub plots and questing. After catching up with the city which is quite difficult with all its shifting through those major planar bleeds. You could have a nice showdown in the city or outsmart them, outbid them, kill them. Make some more sied quests in the city.

The possibilities are endless and yes I'm a plane freak

 

[s/LaSH]

Divide and conquer...

After driving wedges between surface kingdoms, why not go one step further and create massive force walls taller than mountains around every realm? Then you can selectively flood entire nations when they displease you, and shift in settlers when the waters subside.

Also, with the drow driven out onto the surface, you'll be seeing some interesting stuff before the aboleth ever appear. The drow rely on technology that disintegrates in sunlight, so one of two things will happen. One, they'll lose their infrastructure and scatter to all corners of the world, trying to find a new way to live. Or, Two, they'll discover how to bring their technology into the daylight world without it disintegrating, and become a lethal force. The only thing that stops drow from conquering the surface is their daylight vulnerability; if they can surmount that, their blades are sharper, their armour is lighter and harder, and their magic is more powerful. A day-proofed drow army would quickly carve out its own empire.

Finally, it mentions in the aboleth's description that they gain the memories of anything they eat... that's got to be good for a plot hook. Perhaps the PC mage or cleric gets targeted for consumption, or perhaps a well-known, wise member of the community has their head chewed off while fishing. Fishing down a well, just so nobody thinks there's a crocodile or shark to blame. And if they're going to be throwing around walls of force and conditional teleports, they can probably clone some good, clever people and pass them around at dinner. Quite hideous, no?