Was asked to make this cake and have a few questions. She wants it all buttercream so was thinking using a similar technique as doing a fault line to make little indent slashes. What should I use for the blood, red food coloring and vodka? Corn syrup? Any ideas/tips would be amazing!!

perhaps piping gel?  Wilton and Cakemate (available at most grocery stores) sell a small tube of decorating or writing gel that might work.  Good Luck!

I would use piping gel, just because I already have it in the pantry, but a tube of the writing gel would be perfect, if you need to buy something.

I agree with the others - piping gel is perfect for that effect.