When I entered my Slaanesh marines in 2016 and 2017 I put them in a diorama, facing Biel Tan Eldar, fighting for a maiden world. Similarly I’ll be putting my Mentors in a diorama fighting...
A Genestealer cult.
Two classic 2nd edition armies.
Now, I didn’t do a lot of Eldar models in the last AoP as I don’t actually want an army of them, and the same applies to GSC. Just enough for there to be some OpFor in the diorama.
I have some purestrains done from another diorama, which I’ll be reusing, including one getting its head blown apart:

And am now working on a pack of GSC. Overalls and boots will be beige as it should show up the Mars powder nicely. For reference, some of my Mentors:


I plan to do the ribbed bits of their clothing as dark, dirty metal. Add some hazard stripes for colour on plates here and there. For loincloths I’m thinking red - while it is a colour on the Mentors too, the diorama is supposed to be on a Mechanicus world so I think the red will tie them to it.
I’ll post more details and some photos in good time.