I used a boxed red velvet mix for the cake, and whipped up a batch of buttercream for piping the details on – this is the recipe I follow. I would also love to try filling the cakes next time – maybe from the bottom – to add a bit to the frosting/cake ratio (in my opinion you can never have too much frosting)! These would also be great as a molten cake with a ganache filling, as seen here. It's like chocolate blood...so cool for Halloween.
I was going for a linework/doodle look, so I used a #3 round piping tip to create fine lines—you could also use a rose tip to create flowers or roses as accents, or tint your frosting with food coloring. Their website also suggests doing a light glaze or just dusting them with confectioner's sugar. Lots of possibilities! I'm definitely going to have a lot of fun with these, beyond Halloween—skulls are always a good idea ;)