My advice would be to not play with two others- they spawn more enemies, which won't necessairily fight all of you equally. Single player is the best choice, and as many others have said, practice in quick play on the level you're stuck on rather than continually trying to replay all the way through survival.
Right now, I'm at Krang 2. Before that, I got incredibly unlucky on the freeze rays with the enemies hitting me and no way to progress unless I killed two of them. So, with that in mind, I was going to try again in quick play and devise a tactic. No luck. My connection went down and my save got wiped. So, I went through survival again to unlock the levels (and give myself a chance at the achievement at the same time)... Turns out, if you don't rush completely and leave the pizza where the freeze rays start, you can lure the next 3 enemies back off the freeze rays and once they are dead, grab the pizza. Hope that helps in some way.
Wish me luck- never been good at fighting Krang 2 or Shredder, hope the tips here can get me through!! Never been so nervous and close to throwing up because of a game in my life. xD
Done & done. I destroyed Krang 2 without using the pizza before starting the fight or during it, and Shredder? I shred him a new one, whilst using only one pizza and keeping my health full after doing so. Man am I glad this game is over and done with! Good luck to everyone else still in need of this achievement! It isn't so bad once you have some tactics for tricky parts of levels.