Mario vs Donkey Kong
Level 5-5, Section A
Right after the "Here we go!" Run onto the conveyor and duck, keep going left to the edge of the screen. Jump off the trampoline and hit the Yellow Switch. The red blocks will turn into outlines. Next go climb the ladder up and go left to hit the Switch. Then goright to grab the Key, throw it onto the conveyor and then ride it yourself. Now you will come across two elevators, what you want to do is have Mario jump onto the first elevator to reach the second elevator. On the second elevator throw the Key, it will hit the ground but Mario won't. The Key will now have a expiration timer, so quickly jump back to the first elevator and just fall down. Hit the Switch to reverse the elevator's direction. Ignore the Red Switch, climb the ladder up and grab the Key. Take the elevator to the right up and hop onto the yellow blocks. The door is there and you know it.