Yep, that's right, after all this time and threads asking about how to make them, I still dunno how to do so, I can only come up with a sort of mediocre version.
Screenie:

The inner part is just whited, its not Alpha'd at all, that means that if the bg were not white, the inner part of the circle would be obvious.

Screenie 2:

This is what I'm going for.

Leave comments please, also, I used my snipping tool to take the screenshots, upload them on fileize, and post them here. You can do the same, I'm certain every windows vista or more recent, has a snipping tool.

Thanks

Do it like that, but when you set it to gradient to white, there should be an "alpha" setting. Set it to zero. C:

EDIT: The alpha for the color should be ON the character setting.

Subzero is this what your looking for?
http://www.fileize.com/files/a8d727c6/3dc/Impact_circles.swf
idk why i put in the swf but yea its easy to make in my opinion this is actually my first one lol XD

That's not an impact circle in your example, that's just a sword trail arc.
Terk used a circle there because it's simpler and more natural-looking than drawing a straight line and bending it.

Quote from Shensurei

That's not an impact circle in your example, that's just a sword trail arc.
Terk used a circle there because it's simpler and more natural-looking than drawing a straight line and bending it.

so did he like make a circle then make another circle inside of it?

Quote from KidDarkness

so did he like make a circle then make another circle inside of it?

It's just a circle with a radial gradient that has an alpha color on one end.
It's pretty basic stuff, I can put up a little tutorial if you guys want me to.

Thank you for all the comments. I see what to do now.

EDIT: On second though, I also want to be able to know how to do what Terk did.