Just remember, even as with grave and serious sins, even minor sins require the three factors, it’s morally wrong, you know it’s wrong, and you do it anyway. If there is something that you think might be wrong, and you are invincibly questioning the issue, how can you know it’s wrong if you only think it might be wrong? Thereby, with scrupulosity in check, doesn’t look like it would be a sin to encounter that scene in a video game. Also, we have to acknowledge that it is a “fantasy” game, a story of sorts, that doesn’t represent reality nor do they tout any moral message. It’s pure entertainment.
On the surface, we are meant to enjoy the things in our lives, even those brought about the advancements of technology. I see nothing intrinsically wrong with playing video games with simulated violence as long as that violence is not directly tied to moral difficulties. Enjoy the game, play in moderation, and keep in mind that your life is to represent the Glory of God.
Peace.