Hi folks. I've had this come up with players in two tournaments in a row, now, and while I think I know the answer, I want to make sure.

Today's instance had Impulse (on Hypersonic Speed) MOSTLY surrounded by a bunch of Seven Deadly Brothers. It looked like this....

BBB
BIB
_BB

where B = Brother, I = Impulse, and the underscore is an empty square of clear terrain.

Could Impulse have gotten out of this mix by using Hypersonic Speed to break away and move through the intersection to the clear square in the bottom left, or was he stuck there as one of the players was assuming? I'm thinking he could get out, but I'm not sure. . . so that's why I'm here!

From the Players Guide entry on Hypersonic Speed: Give this character a power action and move it up to its speed value. It automatically breaks away and can move through squares adjacent to opposing characters. During its move, this character may as a free action make one close combat or ranged combat attack with its range value halved for the attack. This character must be in a square where it could legally end its move in order to make the attack.

Yea he can because the square is adjacent...
Or at least that's from what I know

A character cannot pass through the square occupied by an opposing figure or a square of blocking terrain. Two squares of blocking would block line of fire and movement, so I am going to say that the same would be true here.

But you can still make an attack through such a square therefore it is not "like blocking" the only way I would think it might work like that is if it was a peanut base.

That's true for blocking terrain. But characters are not terrain, and while they would indeed block a line of fire that crosses that intersection, you would still be able to move through there.

I agree. While both blocking terrain and opposing characters can block LOF, their movement restrictions are very different.