I think a big black witch's hat would be good.

A unicorn. Perhaps charcoal coat color with a sort of silvery wavy long mane and tail with a white and black stripe in the middle.

I'm thinking of making this one a male...Xiee, I love you. that sounds perfect. I'll give him a more appropriate name from a generator soon. CanterlotBrony, witch's hat as an accessory or a cutie mark? I like the idea of it being his accessory, but not his cutie mark (I'm not changing his cauldron...sorry.)

Yer welcome!