I’m surprised you mentioned Diablo.
Diablo, at least or especially the original, means (of course) “Devil,” in Spanish, and your mission is to defeat Diablo in the game. The context is in a medieval setting wherein you slowly purge an old Monastery (going down through its dungeon layers, then through
the catacombs, and finally ending
in Hell) where you battle Diablo, who’s annoying to fight but once you get familiar with his tactics easily beaten assuming you didn’t rush to fight him and are therefore poorly prepared. “Diablo” was unleashed to the world owing to a traitorous minister of your (the player’s) rightful King. This traitorous minister poisoned the (mind of the) King, then kidnapped the King’s young and only son and heir (whom you later rescue). Furthermore, the traitorous minister (Lazareth, if I recall) is highly reminiscent of the Biblical idea of a or an anti-Christ, who seeks to usurp and replace all authority in order to bring the way of the devil for his own profit. He’s clearly a Satanist insomuch as he grovels at the power of his “master,” Diablo, and does this in such a way that it infuriates the player (owing to the minister’s wicked/evil deeds). A young person may actually be a little intimidated by this bravado on the part of the wicked minister, but more often than not the player will choose to bravely push onward confident that ultimately he will be able to defeat/overcome the evil minister and even his master.
Diablo insinuated to me (when I was a young secularist/atheist) some basic monotheistic tenets and religious concepts that were hardly turn offs. Seeing as it was a game, I did not feel intellectually challenged by it nor did I feel like someone was trying to convert me. At its core was the idea of Heaven vs. Hell, Good vs. Evil. I strictly recall that one of the best items you could have was the Silks of Valour (or Virtue, if I recall), which was Roman Imperial-inspired regalia, reminiscent of what Emperor Constantine would wear ; nonetheless, that helped confirmed me (in my youth) about the positive beliefs I had in the goodness of human virtue(s), which was rarely positively encouraged or affirmed among my peers, my educators or in the media (though Gladiator and Braveheart were good for this, at least

).
Games can have all sorts of inspirations, and are neutral like anything, and only become “good” or “evil” when used for either purpose. It is highly feasible that Diablo didn’t have a little Catholic influence, and nothing in Diablo would turn someone off from the Catholic Church.
The Lord of the Rings, for example, could at first sight or glance appear anti-Christian or at least anti-orthodox Christianity, owing to its use of fanciful creatures and fairy-tales, etc, ; however, we know for a fact that J.R.R Tolkien was not a little Catholic, and his Catholicism played a part in inspriring his work and its themes. If anything, games like Diablo and works like the Lord of the Rings are spiritually good for people, and can confirm them inwardly about basic morality, the existence of good and evil, etc., without threatening or challenging them. It can be one small step towards conversion as the reader/player explores these concepts and finds them not only un-offensive but verifiably and positively “good.”
Pax,
Tim