Unreal tournament 3 on insane. I mean without glitching your way to the final boss on casual.
It's impossible. They get near perfect accuracy, double health and double damage.
So any close quarters map is impossible because they pick up the link gun then laser you to death within 0.1 nanoseconds of you seeing them.
Oh yeah, and they can choose where to spawn, so say you have the flag, and killed 2 enemies getting it out of their base. They now will spawn in front of you continuously with a 5 hit kill gun, to such a pace that you'll have to kill them 7 times EACH walking down a 6 meter corridor. And it's all corridor. And your allies suck so badly they basically say "Here, have a free flag and shoot me in the head." to every enemy that comes anywhere near your base. Finally, the enemies travel in packs, so if you kill one, you'll immediately be killed by the other one. Or two. Or three. then if you survive this long, they'll all spawn around you and kill you instantly.