How to make an animated decal GUI?

Depends what u are animating. If you are trying to get some kind of animation like they have in Pokémon Brick Bronze then first get all the different decals you will use. Like each decal of the same thing in a different position then if played super quick makes an animation then put them all inside an ImageLabel and place this script inside the image label.

local Decals = script.Parent:GetChilren()
for I = 1,#Decals do
wait(0.2) --How long you want until each picture changes
if Decals[I]:IsA("Decal") then
script.Parent.Image = Decals[I].Texture
end
end