Game is on Steam for free https://store.steampowered.com/app/1289310/Helltaker/ so you can read about it or play it yourself. Rather than direct satanic indoctrination it appears to fall into the, far too common, realm of media that makes light of Hell consigning it to harmless fiction through cutesiness. It's desensitizing to people who don't know better. It does not appear to be explicit in content (though it did have a character named "-itch" in the video), and the majority of it is probably puzzles not plot. Would I let my young child play it, no I wouldn't. Until a child is grounded in Biblical truth they have no answers for the behaviors and worldview such a thing doubtlessly expresses. While there are worse things (Hazbin Hotel comes to mind) Helltaker's plot is about building a HAREM in Hell. Explicit or not that is not a subject a young child needs to glorify.
Although I didn't find the game on them there are sites which provide Christian game reviews. https://www.christcenteredgamer.com/ and https://www.pluggedin.com/ come to mind.
Also I'm not sure if this is a bot/troll post but since the game is real I thought I would answer the question anyway.
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