One of the simplest ways to get a flaky mermaid makeup look is to use mesh tights or a wig cap. As mentioned on the Cosmopolitan site, running one of these over your head and across your face creates a stencil that you can fill in with makeup.
The specific products and colors you use is ultimately up to you, as you can use a fishnet hack to create a completely different look depending on what you’re going for.
Kathleen Celeste uses products like BH Cosmetics eyeshadow palette and Anastasia Beverly Hills highlighter kit to achieve her purple and blue look (via YouTube). For a darker purple style, shivonmakeupbiz used a mix of green, blue, and purple from various Urban Decay palettes (via YouTube).
You can create an ombre look by flowing one color into another or fading the scales in your skin by using the remaining eyeshadow on the brush the same color as your peeler. While applying makeup, it’s recommended to use the applicator instead of brushing, because you don’t want the scales to work together.
Once you have carefully removed your temporary stencil and revealed your beautiful scales, you can add as much glitter and jewelry as you like to complete your Halloween mermaid look.