You need to use collision boxes. Like if scorpion is punching, you'd create a small box where his hand is for the punching frame. You do this by creating an imagepoint in the image editor on the frame where he punches. Then in your events, if frame = THAT FRAME, then create a collision box. Then you'd check that collision box to see if it overlaps.
There's much more to it than what I've described though. How do you cancel out the opponent's strike if you both hit at the same time? What about frame skipping.. that one frame for the collision box may not be enough, so you'll either need to create it for a few frames, or add a small delay for that frame (in the image editor, you can set delay times for each frame).. and so on..