Start by shaping your cliff with a set of different shapes you created. (either by hand or other tools like VoxelSniper)

Here are some of the shapes I used for the cliff above :


Next step is simple, select your shape and bound to an item to create a brush.
//copy //br copy -p
Select another item and repeat the same process to attach the other shape to it.

Using VoxelSniper commands to perfect the shapes.
Commands you can use : /b e fill /b e lift /b e melt
Can work with better brushes as well : /b eb lift /b eb melt
/! Do not over smooth!

Apply basic colour depending on the biome you want.
Commands: //br cyl ID 6 3 //br sphere ID 10 (combine with //mask >ID)
//br sphere ID 0.8

Additional brushes that will totally change the outcome of your terrain :

Bound each brush to a different item with //copy /br copy -a

Here is the result thanks to the custom brushes used :

Finishing touch using /cs build vine


List of the block IDs used for this terrain :
4, 1:5, 172, 5, 5:3, 35:13, 159:13, 159:5, 159:8, 5:1, 159:7, 35:12

Start by making a sphere : //sphere 30%glass,70%0 10

Color your sphere to make a gradient using //br sphere ID 3
Select your sphere then //copy
Select an item and type //br copy -a

Apply on flat surface by masking surface ID + all the blocks used in the brush.
Just simply use : //mask !0

Repeat until you get the texture desired

Apply on any 3 dimensional surface as well!