Process of panel #4:

Pencil and partial inks. These are done in a high-resolution smart object, which is shrunk down to fit the page.

Background finished. I processed a photo from a tomb and added a little embossing. Colors blend from from “flashback” green to the mud color of the tunnel.

Color flats added to the foreground.

Gradient overlay, cast shadows, and rim lighting added. The light beams are a Photoshop FX brushes added above the lineart.