Alien mission 15 is pretty ridiculous, and I actually have the hard badge. What really makes it harder than it should be is the strict 4 minute limit to beat the level. Going through the Raze Soldier's lives is an incredible pain, and poor spawns will screw you to no end. I'll admit I only got the badge through more-or-less sheer luck. My strategy involved camping the Invincibility and Double Damage spawns and just spamming rockets. Whenever I had invincibility, I'd pretty much pray that I'd run into the Raze Soldier, get up in his face, and hope he suicides while I was still invincible. Sometimes, it takes forever just finding the guy, let alone killing him.