Level two you fight a giant slug/snail thing.
Reset the from last checkpoint this will have the creature closeer to you at the start. Aim right below the wing and across the engine....then fire (Hold RT). When you are going to have to reload press LB for ninja vision and cancel once you reloaded, then continue to fire.
It may take a few tries but I found if you keep aiming under the wing top right corner it hits the most.
Good luck