Nintendo has released a new set of Halloween masks for players to pick up in Splatoon 2, and each one apparently does something different. However, Nintendo didn't make it easy to pick them up as there are no challenges involved to receive them… you have to sign up for stuff. Splatoon News on Twitter posted the full instruction of how you can pick these up, which involves getting three pieces of gear through the Nintendo News App, with your account linked to it, and then subscribing to the newsletter. It's all free, but let's be honest, you'd rather play the game than go through a bureaucratic system for them.
Once you snag them and they're added to Splatoon 2, each one will give you different abilities in the game. The Anglerfish Mask, as well as the Kyonshi Hat, have the Ink Saver ability, the Hockey Mask includes the Ink Recovery Up, and the Li'l Devil Horns come with the Speed Boost ability. Good luck to you in navigating all that paperwork!