[@ColouredCyan] I don't see why everyone is so dead-set on the idea that "Mutant-based powers are the most fair and managable" because, in my experience, it is JUST as open to vagueness exploitation as magic and aliens are. In fact, the worst one of those that I saw was during an X-Men RP where a guy said he had "Hydrokinesis, the ability to control water" and then used that to do completely off-the-wall, bullshit things. I still remember the final straw being him opening a portal which threw poisonous knives of water at the big-bad.

I found that people responded a lot better to the following rules about super-powers. "You can have whatever the hell you like, you be as vague as you like about it, at the end of the day, it REALLY doesn't matter. Just know that everything you do will be monitored by the GM. Anything he finds to be overpowered, he will tell you. If you don't calm it down, he'll give you a second warning, then if the temporature of your mammeries has not dropped by a significant enough amount, the final warning, telling you to stop with the bullshit or you will be asked to leave. And then if they don't stop, you tell that their presence is bringing down the RP environment and if they don't leave quietly, you will ask the Mods to ban them."

Because, at the end of the day, in freeform RP's such as these, everyone's only as powerful as the story demands they be, regardless of what powers they have at their disposal. So, you let everyone have whatever they want, because, sure they can go nuts with it, but they know that'll just get them banned. I tend to play characters that will have a vast assortment of weaponry and skills and maybe powers at their disposal, but I have no problem taking a fall to anyone that asks my character to do so (In fact, I find it is usually more fun to write a character getting the shit knocked out of them than the one that is always fucking people up.) I only argue if I think that the circumstances around taking that fall are a little TOO outlandish or going against the character.

The character I had in mind was kinda a combination of magic, alien and precognition (Sort of like time-travel, but without actually traveling through time) and his involvement with this makes perfect sense and it's easy to fit within the confines of the story you had in mind, because there are only 2 logical outcomes to it and my character's motivations only need minor tweeking to make perfect sense in either event.