See if that helps. Basically don't bother attacking the boss at all. Just kill the regular enemies as fast as you can and then you will get on-screen button prompts to actually damage the boss. Repeat until he is dead.
Hi, really sorry to bother you but I am completely stuck on Ben 10 cosmic destruction. I just can not seem to kill the terracotta lieutenant. Every time I hit his sheild he rebounds me then hits me. Any help you can give would be really appreciated.