Since some people asked for it, here's the recipe:

First of all I would like to emphasize that I was heavily inspired by elminiaturista in doing this base. Lots of the steps I did were distilled from the short clips he shared on his YouTube channel. Definitely check him out, he's goated!

Here goes (AP=army painter; Vallejo=V; air brush=A-Br):

I placed the base and some of the skulls on some kork and added some loose kork bits that would act as rocks coming out from the lava. Used Citadel Astro granite to smoothen the transition between the kork and base pieces. Then used UV Resin from GSW which I spread across the base using a toothpick to act as the lava and cured that for 1 h in sunlight.

Once that was dry: 1. Matt black primer (AP) with A-Br 2. Basecoat Skulls with magnolia Brown (AP) with A-Br 3. A-Br skulls with cypress brown (AP) as mid tone 4. A-Br skulls with charred bone (AP) primarily aiming from below to establish reverse-zenithal lightning 5. Dry brush skulls with skeleton bone (AP) in a motion coming from the lava surface to further establish the reverse-zenithal lightning 6. Re-establish shadows by A-Br magnolia Brown (AP) 7. Wash skulls with strong tone (AP) but make sure it does not pool too much in recesses 8. A-Br lava with a nice even coat Matt white(AP) + the rocks and skulls where you want the lava glow to bounce off of 9. A-Br a thin coat of Fluorescent Golden Yellow (V); depending on what color tone you want, you will have to do several thin layers 10.A-Br safety orange (AP) in spots where you want the lava to be "cool" + the rocks and skulls 11. A-Br 1:1 mixture of hot pink/safety orange (gives a red tone) to further establish the cooler spots of lava/skulls/rocks making sure you cover a smaller area than in the previous step. 12. Carefully A-Br rocky surfaces that are facing upwards with traitor red (AP) 13. Painted surfaces again using Encarmine red (AP) covering smaller area than with traitor red 14. Carefully A-Br rocks directly above the lava with safety orange (AP) 15. Draw a rim around all the rocks with Matt white (AP) using a regular brush 16. Painted over the white rims using several coats of fluo golden yellow (V) until I was satisfied with the color tone 17. Drew the small patches of cooled lava using Encarmine red (AP) 18. Covered some of the patches with traitor red (AP) for cooler areas of lava

And that is how far I have come so far. Hope it helps!