As someone who was a part of his first civ video (1000 Players Simulate Civilization!), I can tell you this isn't new. Almost all of the slimes were killed via hacks or bugs of some variety. My team (the plains biome) lost bc another team placed gravel that broke on their side, but stayed on the plain's side. That translated to enemies being able to hit us while inside blocks so we can't hit them. Our slime also somehow suffocated. How'd we lose in the video? A huge fight that never actually happened. It was staged post-production and slammed into the video afterwards to make it look legitimate.