Just make sure one turtle attacks (bosses) at a time or things can get confusing. Try it on solo first and if you're still having trouble, try co-op.
or pizza I should say.ĮDIT: After playing Survival Mode both solo and co-op, I've actually found that playing alone is easier, at least for me anyway. Yes you only get one life, but if you've played through the game already and payed attention and took the time to figure out the patterns of the game, it's a piece of cake. This achievement sounds harder than it really is. I suggest getting this achievement in co-op, preferably 2 players (that way there aren't tons of enemies cluttering the screen). Just keep at it and don't give up, thanks again for all the support! And as I state later in this guide it is easier to do solo anyway.
I'm not trying to be a prick, but I haven't really played this game in like a year, I would just bring you down probably. That said, I must ask that anyone having trouble with this achievement to NOT message me asking for help. EDIT - PLEASE READ THIS FIRST: I would like to thank everyone for giving such positive feedback, it's cool to know that this guide is still helping people.