Who is this giant spider creature?
I don't want to call him a villain as he's in a picture with Justice League Dark and could very well be a temporary member or ally.
The spider-creature on the cover of Justice League Dark #9 doesn't actually appear in the issue. The creature is probably meant to represent the overall threat of the issue, which are a variety of demonic creatures summoned by Felix Faust throughout the issue. Also, at one point near the end, JLD member Doctor Mist finds himself stuck in a giant spider web and must be freed by the others. However, whatever horror made the web is never shown.
We later find out that
Doctor Mist is actually a mole working FOR Felix Faust. Given this fact, it's entirely possible that Doctor Mist created the web himself and no actual spider creature existed.