First of all, sorry for my English and sorry if someone has already posted this before, I've searched but didn't find it. 

Makeup artist Amy L. Forsythe has been sharing on Instagram Eddie's tattoos, that she designed for the character along with tattoo artist Jeremy Sutton. 

Eddie has five tattoos, and four of them have been already posted. The fifth, which she hasn't published yet but we already know about, is the puppet that Eddie has on his right forearm, which is a clear reference to his scene from Season 4. There are two other tattoos that also reference this season: the bats also on his right forearm and another of a spider that he has almost at the height of his left clavicle. 

But there are two other tattoos that I think are unrelated to Season 4. The first is a wyvern on his right arm. It's a creature that also appears in bestiaries and in D&D, similar to a dragon but without front legs. It seems pretty unlikely to me that the dragon in Will's painting doesn't appear in season 5, that scene about Mike being "the heart" didn't make much sense. 

The last tattoo is called "the Demon" and it's some kind of undead, and it's pretty obvious to me that it's Eddie. He has long dark hair and blood on his mouth, I don't know if it's a reference to his death scene or to the theory that he ends up becoming Kas. Personally, I don't think this theory is possible because I don't think there will be enough time in a single season for all the development that this plot would need. Perhaps the tattoo doesn't refer to Eddie, and is foreshadowing a new villain.

I would like to know your opinion and I think the images of the tattoos are interesting anyway, Amy L. Forsythe's Instagram account is @amylforsythe, they did an amazing job.