So I have been doing some research and have found out there is an Invincible glitch which I am suprised that it is nowhere to be found in solutions so I guess I will be the one to post it. I have beat this game 14 times in total trying to complete it and it is one of the hardest games I have ever played.
To activate Invincibility you need more than 1 weapon, so as soon as you get the staff in the beginning you can activate it. To activate Invincibility open up your weapons by hitting up on the D-pad and hitting X+B at the same time on another weapon. To de-activate it just equipt ANY weapon, THERE IS NO OTHER WAY TO DEACTIVATE IT SO DONT WORRY! To run around with it on you have to jump around alot, and right when you land push up on your analog stick. To read tips on using this glitch or strategies to beat bosses and other units just read my guide on the Master Ninja achievement:
Video: I just wanted to show you the glitch and how it can EXTREMELY help in certain situations. The video was done by Kumar Abhishek