Just something to add about Sigma in Megaman X. His final form can be damaged with the gun you get from the Armadillo (I cannot recall the name right now - it's been too long since I've played this game). The dog and Sigma's first form are cake. The best way to kill the dog is to immediately fire a hadoken when he jumps to the left wall. He will land and get hit, instantly dying in the process. As for Sigma, the best thing to do is use the Electric Spark gun (from Spark Mandrill) and wait in the top left corner. When he's about to reach the corner, drop down and shoot to the right. On the ground, wait a second until he hits about midway up the wall and shoot again to the right before jumping onto the wall.
