So, this is a pic I collabed with  dearshul77. Her characters, Moth and Bottom, in an alternate universe under the sea. Moth is a sea witch, Bottom is, or rather was, a merman.
Moth and Bottom have a pretty unhealthy relationship. Moth is . . . well, Moth, and Bottom is an overly clingy, emotionally codependent alcoholic (I think, that's the impression I get from what little I've seen of the character and the few things Dearshul has told me about him). In the webcomic Dearshul is making, Bottom continues to pursue Moth even after she dumps him, constantly trying to win back her affection.
In this timeline, things go somewhat differently. Since Bottom needs to cling to something so much, she gave him something else to cling to: the sea floor.

Hoo, boy this one was complicated. I decided to try exploring the techniques for lighting and shading that I was developing in one of my previous pics and it took me a long time to get down. The actual steps to lighting aren't that much. Thanks to some other discoveries I made about how sublayers and grouping work, it's actually pretty straightforward to get lighting effects to stay on objects and figures instead of just being free-floating blobs of light, but it still takes time. And, of course, I have to know where the light should go. Thanks to  cecaeliafanatic for helping me with getting the lighting righ on Moth. Bottom I did mostly myself, and he's less lit up than she is, but Moth is more in shadows, so she needed the more dramatic lighting to give her enough contrast to draw the eye.
I did run into some other lighting problems because of how vector art works. I drew some of her tentacles as different shapes to make it easier to do the lighting, but that had this odd effect of creating thin, but super noticable black lines where the shapes ended. Fortunately, my program (Affinity Designer) has a pixel mode, so I was able to use the pixel tools to blend those together. It wasn't a perfect blending, but you don't spot it unless you look really close and know what to look for. I figured I could let it slide because the pic won't display at a size large enough to make it visible. Barring learning new ways of using the tools, I think this is the best I can do.
Now I just need to learn how to tell where the lighting should go without being told.