I am currently running into an interesting problem. The current way how to stop a giant robot from within is to find strange symbols, put them in the right order in the main CPU in the middle of the level and escape before the self destruct happens. You can also cause havoc but thats roughly it. Yes there is a timer when the robot will reach the city but .... i am not sure.
My main problem with that is that it does not convey the feeling of fighting this robot and its systems while the robot tries to fight back. Yes there are enemies but its vey linear and thee is no real struggle beside that you might die and lose the level.
That got me thinking. Maybe i need to have a bar on top which can go back and forth. The more damage the player causes the more the bar fills for the player. The robot will react and the closer its to beating the level activate system to fight you back (almost like an immune system) where also the bar can go lower. So its a back and forth and you just have to play well (one big blow will be destroying actively its core (not just typing in a code) to win the level.