Ooh, I love Welcome to Night Vale! What I've seen most Cecil cosplayers do is use a nice brand of face paint for his eye and usually use a stencil, then work around that. I'm less sure on what you would do for the tattoos. Most people use Sharpie markers from what I've heard, and I don't know how safe that is for your skin, but it looks good. If you're a good artist, then I guess you can attempt doing it yourself, otherwise have a friend do it. His tattoos are usually the really intricate tentacle and eye designs, so try using a reference. Good luck!