For the kraven skip i have found a way to skip directly from the start of the gun area to the courtyard. All you need to do is turn back and jump on top of the door frame thing then web jump off and into the fall plane and if you hold forward and the jump button than you should get out of bounds then you web sling along until you hit the load box for the court yard then boom you did it. The one problem with this skip is it might only be possible on the wii.

the sandman skip works. all you need to do is web swing past the out of bounds platforms and just repeatedly hit the fall plane until you get behind the area where you fight him then just go up again and it should load in the next area skipping the boss fight