Witch Blast is a free roguelite dungeon crawl shooter heavily inspired from Binding Of Isaac. The player plays as a novice magician in a dungeon who is trying to get as far as he can, using various items he can find to defeat the inhabitants of the dungeon.
As the title says, I find "Closed source" a bit hash of a classification for a game with GPLv3+ code and CC BY-NC-SA assets. As much as I dislike the NC clause, and would indeed consider the assets nonfree to some extent (at least not DFSG-free), I think have GPLv3+ code and "partly free" assets should be enough to tag is as open source.
All in all, we really need an "Open source with nonfree assets" category for such cases...