The problem with non-strength Immobilize is we have NO CLUE on how to impliment it mechanically. The rules say it is possible, but provide no guideance at all on how it should be done, or what the effects should be.
Just subbing in the word "Mega-Dex" or "Willpower" for Strength results in powers that are totally, horribly broken and confused as too what they do.
For the given example above Immobilize(Willpower)... what does this mean? How do I resist it? How do I damage it if someone else is caught in it? Immobilize has soak, how does that work? Does it still reduce Mega-Dex?
If it is resisted by Willpower instead of Strength, then with a willpower of 10, I probably have no serious chance of breaking free because of it's soak... how ever, someone else could still blast me free with a quantum bolt because external people can help break people free, and the effect isn't intangible.
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Hauling things through the sky.