Regarding the unicorn: Why not print a Narwhal and then cut the tusk off to "kitbash" a regular horse into that unicorn? I mean, why make it simple? If you want simple, almost any "spike" can be attached to the forehead of an n scale horse. Making it from a Narwhal at least has some historical significance.
The real problem is going to be generating that hologram of a rainbow to get the right "look" to those farts.