I thought I'd suggested something like this once but...
I stumbled across the Darth Maul horn-cap piece, and I was wondering why more wasn't done with this idea. Imagine a similar "cap" that gave a minifig underslung ram horns. Or classic devil horns. Or maybe even big Hellboy/ Loki sized horns. It'd work with yellow, to match minifig "skin," but there are enough heads out there in black, green, red, white... there'd be room for many versions. Even more if the cap itself was painted so the horns stood out as a contrasting color (red horns but a yellow "scalp" if that makes sense).
Just more random ideas.