Nice project idea, keen to see the result!
I've done some tests mixing small amounts of brown paints with Nurgle's Rot and the resulting gooey mud is quite interesting for this kind of theme (or for sewers), it's worth playing around with the stuff! I'll try and find some photos when I'm back from travelling.
Stirland mud is quite interesting as it has a wet look with a dark brown tone, such as that of gravel/volcanic shores - probably quite fitting with the theme rather than paler, sand colours.
For crushed vegetation you may have some success by drying some grass, leaves, small leaves from the garden/park between tissues in a book (as herb collectors do) to preserve some of their colour, for a good few days (so they lose most of their humidity but remain flexible) and when you add them to the base with a texture paint /paint they'll get wet and will be easy to shape to look crushed (they're less rigid than plastic). You'll need some sort of varnish though to secure them and preserve them.
You may even recover some fish skulls form tiny fish (eg those used for fritters, small sardines, etc.. from your favourite fishmonger) by cooking the heads for a good hour and cleaning them carefully with a toothbrush, then drying them. They may need a quick rinse with a bit of dilute bleach (and a copious rinse with water afterwards) to remove the smell. And some varnish. Never tried it but certainly an idea worth looking into, I way contemplating doing this for some Troggoths but never got around to doing it.
If you have an AoS player around they may have bits from the troggorth kit that contain fish bones and angling items.
Those are the ideas that pop to mind right away. The project is certainly cool!
Edited by Isolia, 14 February 2020 - 08:47 AM.