here's how to get to the mission: http://www.gamefaqs.com/console/xbox360/file/944262/58302
Easy way to beat this mission is this: (Normal)
Buy any quad-legs, but DUSKAROR-LEGS are the best choice, although any can work. Equip GANO01-SS-WBP and GANO01-SS-WBP. Quick Boost (ground) until you reach Great Wall and keep Quick Boosting near the right side of Great Wall. Once you are behind him one shot each obstacle. Once inside ignore all the enemies and just blow the doors heading to the front. When reach your target, blow it up and zip back out the way you came zip with OB. Piece of cake.