Shao Kahn is as cheap as you can get in this battle. For me, teleporting behind him didnt work because there was too much distance, and Raiden's reach is short. So instead, I either backed myself into the left corner or flying attacked him into the right corner, and blocked most of his attacks while doing the square, triangle, square, down+back+ triangle combo as a counter. You only have a very short time window after you block his attacks, and NEVER attack him after he does his forward shoulder charge, because his recovery is too fast. And use the xray move as soon as possible.

same way you beaten him the first time (if you think like me that is) SHOOT LIGHTING BOLTS ALL DAY!!!!!!!!!!!!!! he get next to you run!. he taunt so much you will get away. =]

I'd imagine it depends entirely on the difficulty level you're playing on. I did medium (which I found suprisingly difficult in the later stages in the game) and to defeat him I stayed far away. He'll start throwing spears (duck those) but when you see him start to throw the sledge use the teleport uppercut technique mentioned above. When he throws the sledge you'll teleport close enough to him to hit. You can try to teleport before the arrows but the distance is a bit off so it'll work maybe 50% of the time. Patience is the key in this one.

What I did is switched it to easy, then you get as far away from his as possible and just lightning bolt him over and over again, if he throws spears just duck, then if he stops throwing spears lightning bolt him some more. If he throws the hammer you just teleport and uppercut (down triangle/ Y). Then when he taunts you do the fly move to him. Be carefull though, once you do the fly move all the way to one specific side, after you do the move you dont leave much space between you and him, so if you get to the very edge of the map and he taunts, just keep lightning bolting him and move back away from him untill theres room again for you to fly hit him when he taunts. Im not sure if this will work on medium though, it should, you just wont get as many taunts out of him.