During the last fight with Solidus, before he sheds the tentacles from his suit, you can run off the side of the building and hang on the ledge. Solidus will come over and say "What are you doing?" and go for an overhead double sword strike. When he does this, press the button to climb back up and Solidus's attack will go through you, giving you a free shot at him. This can also be done to avoid his homing missiles, but you must climb back up at just the right time to avoid all four.