In the Boss fight where you must defeat Shredder, instead of focusing on the 
many Shredder clones, try fighting the real Shredder. He just stands still while 
his clones fight you. One attack that works well is Don's team move that shocks 
any enemy near its radius. Get near him and use it. It will shock the clones and 
him, and he will not be able to attack. Change to Raphael (because he fights the 
hardest) and attack Shredder a few times until he recovers. Once he recovers, 
repeat the steps until he is defeated. After this level, the Foot Clan will 
appear. Use a similar tactic when a Foot commander calls in more Foot ninjas as 
you defeat them. Use the same tactic on him. If you do not, he will overwhelm 
you with lots of Foot ninjas.