The last battle of a Combat Tour is the hardest. If you end the second to the last battle with most of your health, do not pick up the health icon that appears. Go to the last battle and fight. If you are low on health, simply webswing back to the area of the previous fight and the health icon will still be there. Take it and return to complete the last challenge. Also, make sure to spread out the enemies and try to lure some of them to other areas. Some will follow and some will stay behind making it easier to fight them.