hi guys i'm making a halloween theme birthday cake and they want one like in the picture below. how do i get the blood effect any ideas are much appreciated. thank you

No picture so I don't know what it looks like, but you could use colored piping gel or royal icing.

I used red gel in a tube and darkened red candy melts.

If you want a real blood look I'd use something like piping gel or maybe even corn syrup colored red. It will be translucent.

I agree the red dyed corn syrup works really well, it has the consistency of blood.