The main thrust of the overall plot for this scenario is that there was once a colony of the cambions’ Red Pact on the hill, and then it was abandoned. That was 200 years ago. Now, the barren hill is being covered by flora and fauna of the Tartarean Sphere as the cambion are returning and terraforming it.
Here are some delightful B/X monsters reskinned for Crumbling Epoch with an eye to being consistent with the design aesthetic of Devilmount mixed with my own style.
If this does not creep you out a little, I fault your imagination rather than applauding your courage.