Scratch

hi all,
I've done a WWII game. You are playing an american soldier and have to kill Hitler, it just has 3 "levels" and there are only 2 enemys (German Soldier and Hitler himself).

I would like you to tell me what you think about my first project and give tips if you can 

Hitler for example is in every level at the right top of the game, because i dont know how I can make him invisible till the player's sprite is in the room where i want hitler to be and shot 

If you play the game you will see what I mean