how do i get this chocolate effect? is it dipped in ganache? is it buttercream underneath? it looks so perfect!

It looks like a version of Hi-Hats: http://search.aol.com/aol/image?s_it=topsearchbox.image&v_t=wscreen50-bb&imgsz=&imgtype=&imgc=&q=Hi+hat+cupcakes

but they didn't dip all the way to cover up the yellow icing.

Also, I think most hi-hat recipes just use melted chocolate with a few Tbs. of oil to thin it out vs. ganache.

Yep, Hi-Hat. I've done then. Pretty easy. Just regular dipping chocolate, aka Merckens.