We broke the Anima system in half with overpowered characters. Not that it holds together very well normally. One mage character boosting the tank's strength high enough to lift a mountain and creating him a giant tungsten lump, another mage opening a portal directly above a bad guy's tower, apply tungsten to tower at great speed. No more tower. The GM was too amused to be mad that we wrecked his whole plan. We used the same trick to launch a necronomicon into the sun (or near enough). Also so many magically created artefacts, creation mages are just bullshit. But I got away with it because I made some for everyone.