Alright, this is quite a simple one, but adds some immersion to Nightmare buildings and Ancients.
This texture is used for both birth and roots effect.

Bad news is... that Blizzard decided to separate the same texture for ALL Ancients.
This means you'll have to import multiple instances of the same texture over and over and change it's path (see below):

buildings\demon\corruptedtreeoflife\nightelf_buildup_diffuse.dds

buildings\demon\corruptedancientofwar\nightelf_buildup_diffuse.dds

buildings\demon\corruptedancientprotector\nightelf_buildup_diffuse.dds

buildings\nightelf\ancientoflore\nightelf_buildup_diffuse.dds

buildings\nightelf\ancientofwind\nightelf_buildup_diffuse.dds



The actual birth texture has this path:

buildings\nightelf\nebirth\nightelf_buildup_diffuse.dds