what i don't understand is that when you get to the enmies castle the enemy spawns a billion units and has them get charging at you. YOU can't do that!
i think i got the key for getting more upgrade points. when your in a level you kill all enemies but one, and let that enemy kill all your heroes. then you will restart the level with the increased exp and upgrade points.
i think i got the key for getting more upgrade points. when your in a level you kill all enemies but one, and let that enemy kill all your heroes. then you will restart the level with the increased exp and upgrade points. + me if you think i'm right