Silverfox
Literally all she had to do was get within arms length of Stryker, and she could have gotten her sister out of prison. That's it. Instead she tricks a deadly mutant into loving her, fakes her death with a common diuretic (what? I don't even...), reveals that she's actually alive to him, and then dies for real. Way to go. You fail at everything.
But at least she used her powers for their God-given purpose: asking a couple of Canadians to move their cars, and convincing her arch-nemesis to go Forest Gump for a while until his subordinates tell him he's under investigation for murder, which obviously went nowhere because he's still in charge of a big government mutant program in X2 so there was literally no point in showing us that end scene at all anyway.