It's not even +66% against anything other than ore trucks. Or stolen mammoths/MADs. It's only +33% against other MBTs, the APC and ML, and no bonus against light vehicles - which, yes, is intended. The mammoth honestly does not need any help taking out light vehicles, even phases. Raising the "pure damage" of mammoths any higher than it already is will just make them even more OP. Just like heavies, they kill rangers and arties in 5 shots, and are just a few damage points away from being ab