Li'l Devil Horns

Appearance
The Li'l Devil Horns are a plastic headband with horns and a battery compartment behind the wearer's right ear and a smaller compartment between the two horns. The horns are lit up from the inside, making them glow in the dark.

The wearer will also have small gemstones on their face, the placement and appearance of which change depending on gender. Female Inklings and Octolings have patches of many gems varying in size and color below both eyes, while males wear two pairs of similarly sized blue gems, one pair below their left eye and the other above their left eyebrow.

How to obtain
If this does not work, start over at step 1, or view the video demonstration below. https://www.youtube.com/watch?v=NMJiEkaXgp4
 * 1) Open the Nintendo Switch News application and select the article about Splatoween.
 * 2) * The article is titled Free Download! Celebrate Splatoween with this spooky in-game gear.
 * 3) * If the article is not visible, subscribe to Squid Research Lab Report (NA) or Squid Research Lab Bulletin (EU) and allow time for the news application to update with Splatoon-related news.
 * 4) Select the "Happy Splatoween" button located at the bottom of the article to start Splatoon 2.
 * 5) Open the box that appears in the middle of Inkopolis Square.

Trivia

 * The Japanese name for the Li'l Devil Horns, translating to "Sea Slug Headband," refers to the horn-like rhinophores of sea slugs and other gastropods. As nudibranchs are suggested to exist in the world of Splatoon, Inklings and Octolings may wear the headband in reference to them instead of horned mammals, which are likely extinct.
 * The Russian name for this gear seems to have been confused with the translation of the Anglerfish Mask's name, probably due to both of them being released for the same event.