Timothy Paradox

All I remember was being in a building, and fighting a video game 'boss'. The whole setting was 100% realistic, not all all like a game, but I could retry the fight as often as I wanted. The boss was just a person, but taller and very strong. Conventional weapons didn't seem to hurt him very much. I had this bomb, it looked like a German stick grenade from the second World War, but it had multiple explosives. I say 'bomb' and not 'grenade' because this thing was utterly devastating. I think I put the grenade in his backpack (or somehow attached it to his back) while distracting him. Then I ran away very fast. The explosion pretty much vaporized the large, multi-storey building. I assumed this killed the boss. I tried that fight a few more times. At some point, the explosion happened underground. I ran outdoors, yelling to people to flee as fast as they could, as the blast radius was easily a kilometer. We were on the street when the bomb went off. The ground literally started cracking open, releasing hot gas from the explosion. Someone yelled at people to avoid the cracks.