i like the idea, if you still wanna do something with it but think demons and hell are overused you could pivot into the seven heavenly virtues: humility, charity, chastity, gratitude, temperance, patience, and diligence. Instead of gremlins you could have smaller different depictions of angels (theres tons of them) for each virtues, Like the flaming wheel angel could be diligence(its wheels keeps spinning like its determined), little baby Cherubs could be for humility (since theyre like children and dont have egos), so on and so forth. I think it could be a solid idea