Makeup makes the costume
These make-up effects were created at our shop in about half an hour. There are no special skills required, but a sense of humour helps, and a strong stomach for blood.
Just Imagine stocks latex, paints, and many types of very realistic fake blood.
You can also apply instant wounds made of silicone, then all you need to do is add the gore.
For zombie effects, remember these characters are dead, so a pale skin tone and dark purple circles under the eyes gives that effect. Pick up some blood by the ounce, or by the pint and go for it!