Natural Consequences

Some things just do not work well under certain circumstances. Cinder surrounds herself with flames that she creates and controls. Yes, she can produce enough heat to turn water to steam... but she doesn't know how to control steam, just fire. Throw enough water at her quickly enough, and she has two options: Let her fire go out (in which case, she gets knocked around by the water, and can't keep herself aloft) or apply rnough heat to evaporate it all (in which case, she gets knocked around by the veritable explosion of scalding steam). She doesn't much like either option, but it's a simple example of vulnerability by natural consequences. In similar veins, some speedsters have horrid habits in the snacking department - their bodies burn fuel too quickly.