What comes first to mind...
- Magic: the ultimate plot device. Really, there are a lot of open powerset plot devices out there (eg, power cosmic), but magic seems to be allowed the most freedom to do anything. I believe even Galactus once stated he feared magic or didn't understand it.
- The problem I have with the speedforce is this: while it is a good way to explain how speedsters avoid superspeed pitfalls (eg, inertia, friction, relativistic effects), it also involves apparently arbitrary abilities (eg, speed stealing: I guess someone thought moving fast w/o limits wasn't enough of a power), and it is applied in self-contradictory fashion. Case in point: if the speedforce protects from relativistic effects, how does Flash generate an "infinite mass" punch? And even if he can "selectively" apply relativistic protection, 1) how does that keep his body in one piece; and 2) why doesn't his fist become a black hole? Clearly, the speedforce is being pushed to become another open-powerset plot device.
- Female counterparts to male characters simply for an "equality between the sexes" thing. Stop it. Just make original female characters.