To summon the blue fairy, simpy press the button combination ↑ ↑ ↓ ↓ ← → (up, up, down, down, left, right) at any time in the game to use the blue fairy spell. It works just like those old Tomb Raider cheat codes. But you only get to cast the spell one time, and so after that, you must visit a save bell and save your progress to replenish the spell for reuse. Also, you can literally perform this spell at the very beginning of the game, and so it is useful if you are stuck in a bind early on. And remember that you can always recharge the spell whenever you visit a save bell. Hitting the save bell also recharges the spell. That's all there is to it! Have fun!