Chain of challenges, episode 17.

We are keeping the background idea only, and we will practice some aerial (atmospheric) perspective, but...underwater.

Pixel an underwater landscape with at least 3 planes of the background. For example, if your background will be coral reef, you need to add an another layer of it in greater distance, and then another one even further away (just like you would do with mountains on the surface). You have to apply the rules of atmoshperic perspective, which means that objects do not only appear smaller, but are also less detailed, saturation and contrast goes down with each layer and there is a colour shift towards the last plane. If your water is blueish, it will shift to blue. If greenish, it will shift to green. If you are willing to go experimental with other liquids in tanks, other planets, fantasy, or something crazy like a sea of pink perfume, you have the green light.

How well you will execute the "aquatic perspective" will not be a factor in mods decision about  accepting the piece to the challenge, but it most likely will be reflected in the vote results, so do your research or ask your friends on discord for help if you are not sure of anything.