Not sure if repost but Basically imagine a Giant Trojan where you have to break off pieces of armor to get to the targetable area. Much like you have to hit a standard trojan in the back you are just breaking down the massive trojan's armor. until you can hit the certain area.

Also if you want to make it harder you could have trojans spawning out of side gates or something to liven things up abit. It could take place in a coliseum or something.