a lot of my friends were having trouble with Mothrakk (the really big flaming rakk in the arid badlands) but i had no trouble at all. i had a soldier and in co-op its pretty easy when someones shield runs out he can just run away and mothrakk wont follow and the other guys can just keep shooting. in single player i only did it with a soldier so yea. ok so i got a machine gun runner car and put it kinda close to the spawn place with the torches after that i lit the torches got in my car and started shooting at mothrakk when my car had like 50 health or shield or whatever i ran away and put the scorpio turret on (invest in the ammo recharge and health recharge things) and started shooting again by then mothrakk had like 45% health and i used an assault rifle and shotgun and when ever my shield was down i just ran away and for some reason sometimes he followed me and sometimes he didnt and basicly i just kept doing that until he died unfortunatly i killed him when he was over a mountain that i couldnt reach so i didnt get any loot :P hope this helps anyone