I don't understand how you're stating it's 99% impossible to beat #12. You just gotta use the right ninjas (doesn't even have to be rare ones or anything), since you can counter everything. on #12 it's usual to kill the ninja which is the most threat with your 3rd/2nd team then go all out with your main
Only lost one #12 so far, but that was only because I was playing * as hell