Lets start another thread about tricks--i seriously think we should have another thread entitled "Tricks & Tips" where people give advice or have discussions about actually designing dungeons, puzzles, overworlds, etc. (like at purezc.com)
Anyway, here's some tricks for ya:
1. Ever notice how when you blow the whistle on a certain space & secrets appear but nothing happens to the actually space that you're on? In other words, there's no "secret combo" for the whistle trigger flag. Well, you can assign a completely transparent screen to layer 1 or 2 of the screen you want the whistle trigger on. Then you place a "secret tile" flag (such as flag #16) on layer 1 or 2, above the whistle flag, and then set that secret combo to whatever you want the tirigger to look like after the whistle is blown
2. Not really a trick, per say, but you can have a dungeon where certain "passages" side warp to the very beginning! This would be great for like a "fun house" type level
...I'll have more in a little bit--for now, you guys can discuss these two ideas or brainstorm some more!