My process of creating these portrait assets for the pixel asset jam I joined recently, starting with the dark element. 

Starts off with a simple sketch to give me a general idea.

 

Then the lineart.

Then I block in some of the general values (lights and darks).

Add some color, a gradient in the background, then just render the hell out of it until I'm satisfied, working in PS using the brush tool creates a perfect pixelated gradient effect when working in a super small document size, though I'm trying not to rely too heavily on it.

Final render, brush tool used for highlights.

thats a cool workflow, i like how using PS influenced the way you rendered things, i dont think gradients like that would be doable with “normal” pixelart tools like aseprite

I think I had understood what made me think that it is AI. Too many "shades". Almost  1 pixel shift = 1 shade shift (which is usually not considered as pixel art... but ok....)