Maybe add some compatibility with rampant with the way bugs dig into sub surfaces , as rampant already has burrowing enemies , im not sure how that would work mechanically but it would make for great and interesting gameplay

But it would look great if you can see the burrowing enemies from afar like an rampant and of they hit a subsurface lvl thats dug out they pop in there , else regular rampant behavior they pop up near a structure on the surface

This mod is quite complex, so please give me more explanation on which enemies dig down and some behaviour of the mods enemies

It doesnt exclude any type of enemies basically same mechanic that the bugs use to form attack groups, they form an attack group of whatever bugs are nearby and then once they are ready to attack they burrow down until they reach a structure i loaded up an old save to show you (check the link)

This is controlled by the rampant "AI: Underground attacks" settings

https://youtu.be/488y6TIDgkE