I've found that anyone who can double jump hit effectively that isn't also chonky, or are even moderately ok at chicken can pretty effectively prevent Iron Golem from doing anything. His huge hitbox prevents him from hitting back properly-partially because of Mineplex combo hitreg-and cannot use his fissure to being lifted off the ground while being hit, and even if you're spamming the fissure button, you usually won't have aimed it properly. His Seismic Slam doesn't really help much, because it doesn't activate for a certain amount of time even if you're just sitting on the ground, and the Iron Hook has a decently long cool down, allowing plenty of time for a combo. I don't have huge amounts of experience with the game, but I've been used Golem for my last achievement (100 Free Kit Wins), and while usually I can handle the attacker alright, there are some ridiculous moments where I just feel helpless. I'm thinking maybe 25-50% knockback resistance. Note: He's also very easy to knock off the map in general, even with his Seismic Slam.