So, something like this?
Cataclysm can shift between a heavily armoured SPG (http://www.army-guide.com/eng/product4029.html
) and a towering mecha form, bristling with Point Defense Laser Arrays and armed with 2 massive shoulder mounted energy cannons. He specialses in wholesale destruction and damage, either over a large area, or against a single target. Should a target somehow manage to reach melee range, he carries a large Energon Mace, which he will happily use to crush anything that poses a threat, or might pose a threat, or is in the way at the time. While he is more that happy to brawl with anyone, getting him to stop on the other hand can take a little effort.
Cataclysm prefers to engage targets at extreme range. Not out of any from of cowardice, but because the longer it takes someone to stop him, the more he gets to destroy. There are those who suspect that he has Decepticon sympathies with his love of destruction, however they are wrong. Cataclysm is loyal to the cause, because this cause allows him to bring his weapons to bear of those who deserve it.
Cataclysm was created as all Transformers are. This tale is nothing new. What was different here was an unusual "flicker" in his Spark. Outwardly he was as normal as any other, but inwardly he was damaged, broken even. He thought little and acted much.
Intitially he was almost drawn to the Decepticon side of the war, his easily led nature and incredible power a big lure. But the Autobots reached him first. Since that day, Decepticons have fallen in droves before him and will continue to do so.