Xanadu

While in a battle or outside, press F1 to pause the game, then hold Shift and press G, R, 2. If done right, your energy will fill up the next time you sustain a hit from an enemy.

Start the game, go to the right and down the stairs. Let yourself drop all the way down. Now, take 5 steps left or just walk left until that long hole you dropped from is out of the screen. After it's out of the screen, go right and you'll magically reach a hidden shop.