The actual Horns hat it’s a good one
But it could become a Epic or Legendary hat with the next additions:
Adding the 16 colors of Minecraft, right now it have only 3 colors(Red, purple and Yellow/Gold) all of them have a black part, adding the rest of colors could be a good idea, they will keep the black part, but with the rest of colors and a RGB variant could become that hat in a Legendary Hat
Adding more colors could make that hat Epic, but to make it legendary could have some Animations, like a shine like lava does or a gradient glitter effect
Those details could make the Horns Hat the first Legendary Hat
Basically: 16 Horns color, 1 RGB color and a gradient glitter animation 
