Assassins creed theme running throughout is the idea of finding pieces of Eden, the apple, etc. Diablo is Christian based upon the heavens, the hell levels, purgatory, the existence of Baal, Diablo, among others. Archangels and the light (representative of God), While it does borrow from other faiths in parts the core of it is Christian religion. Explaining how it is christian based is kinda like explaining how the Lion the Witch and the Wardrobe is christian symbol, you would need a lot more time and effort than I want to put into a forum post.