WOW. Just had an AWESOME Advanced run on No Mercy.
Me and one of my friends who just got the game were playing through Advanced (he hasn't even played Normal) and we couldn't beat the finale. So 3 of the 4 of us stayed on the first roof, where the ladder to go back down to the saferoom leads. The 4th guy ran and placed propane tanks/gas cans all around, healed up, and called in the chopper.
We tried to cover the 4th guy as long as possible, but he inevitably dies. As the first tank approaches we unload on him but sadly our Francis gets knocked off of the first roof onto the normal roof by the tank. While the tank runs off to finish Francis off me and my buddy run back down the 2 ladders and back to the saferoom. We hold out there for a bit, then move to the long hallway and take out incoming hordes with our sniper rifles.
The 2nd tank now comes, and we book it back down to the saferoom, and the tank incapacitates my buddy, and I leave him to run back to the roof. The tank stays and kills him, while I'm waiting on the roof. Then, when the tank is climbing up the ladder I just stood ontop of the opening and he can't move. at all. That's right bitches, 1 vs 1 against a Tank and I took him out with pistols. The glitch (I guess?) prevents him from moving, and the infected don't just "back off" of the person they are going after, especially a tank, so he won't go back down the ladder either. After like 5 damn minutes of pistol headshots he dies, the chopper arives, and I jump to safety.
tl;dr
Finale of No Mercy go back to the safe room.