Well keeping in mind I'm not overly familiar with Power Rangers, but I am familiar with the basic concept and all. I've been a peripheral fan for years.. as I've said to a few peoples, I love the idea of Power Rangers, just not always the execution. So if I flub something here, lemme know.
But here's my initial idea for my character. Maybe the main baddie isn't out to just all in all rule the earth. The main baddie wants the powers of the 'good' rangers, to maybe absorb it so it can be used for baddie purposes. So my character actually gets one of the Ranger's powers, like maybe she's one of the first chosen. But before she can make anything happen, she's mind controlled or otherwise influenced by the main baddie. So she becomes kind of the field lieutenant.
To lure out the other Rangers, she sends the faceless troopers out to the city to start wreaking havoc and killing whatever is in their way. But she doesn't appear yet. The Rangers come out and beat some ass, and that's when my girl makes her appearence and attacks. She maybe starts to win or whatever, but eventually needs to retreat. And that's how we get things rollin.
So not to sound arrogant or anything, but mebbe my character should be more powerful than any single Ranger. Ya know, to actually seem like a real threat. But she'll also be ruthless. But that's only when she's under the control of the baddie. When she becomes 'good' or whatever, she'll be just as powerful as the others. She'll also be under the influence of the baddie when she's in civilian mode. She'll be trying to figure out who the Rangers are to try and get them by surprise.