"I'm really paranoid about using other people's artwork as icons, just a heads up."
You should ask permission to the artist and if they don't reply back then don't use the artwork. If they say yes though, you should credit them when you use it and if they say no, then obviously no.
Or just use the official artwork/screenshots/pictures from the game itself and make edits out of it. (Aesthetics, Collages, etc.)
You don't always have to use artwork as an icon.
Hope this helps. xx