[quote name='Monsta Mack']I take no credit for this as I found it posted on GAMEFAQS...
'I tried posting this in its own thread earlier but realized I skipped a step. I have 4 player accounts on my xbox and all 4 now have it (only one is on xbox live however).
Step by Step guide on how to get Turtle Soup:
1) This method only works offline and you must have 4 players start the game. In the first level have three of them die, including the account that you want to get the achievement with. DO NOT KILL ANYONE with the account(s) you want to get the achievement.
2) Progress through the game until you get to Krang with one player. When Krang is near death bring back all 4 turtles and kill krang. Try to get the turtle/account(s) that is/are getting the achievement close to death before you kill krang.
3) Upon killing krang make sure that all 4 turtles are alive when shredder comes through the portal
4) He will split into 6 clones of himself. Immediately allow the turtle/account(s) that is/are getting the achievement to be killed without being shrunk
5) Proceed to kill all of the clones with the other turtles that are not getting the achievement, this is done easiest with only one turtle alive playing as leonardo or donatello
6) When it is just you and the real shredder keep attacking him until his helmet comes off
7) Once his helmet is off bring back all 4 turtles, his helmet must be off because when it is he will not use the shrink ray
8) Once you bring back all 4 turtles he will again split into 6 duplicates of himself
9) you may now kill the real shredder, but not with the account(s) who are getting the achievement
10) Enjoy your new achievement
Note: DO NOT KILL ANYONE throughout the game with the account(s) you want to get the achievement. In fact, I didn't even move the turtles who were getting it. Just make sure to bring them back right away when they die before killing shredder and krang. Also, this method works both while connected to xbox live and while offline but not while in a multiplater co-cop game
As I said, I verified that this works on 4 different accounts. Twice I got it with raphael, once with Leonardo and once with donatello. Twice I did it with only one account (neither of which were on xbox live) and this last time I did it with the two remaining accounts, including the one you see below.
Good luck to all and YOU ARE VERY WELCOME'
CREDIT GOES TO morning_red from another msg board and this can also be done with two controllers. If you don't have two controllers or more Again this can be done with two controllers. While this might seem to be a pain in the ass, it really isn't. Just get to Krang and load the guy who you want to get the achivement as soon as Krang is down to very low health, kill em, then get killed by shredder...not too hard to do at all.[/QUOTE]
So wait, this can be done with two players instead of four in a local game? If so, I'll give it a try. Thanks for the post, since this one's been driving me nuts.