The second Legend of Zelda game is the only one with this weird experience point system. Get enough points and you can level up your Attack, Life Points, or Magic Points. And, after a while, it takes a lot of points to get to the next level. Thousands of 'em, in fact.

But, if you go to the end of one of the Castles and set a jewel in the statue at the end, your experience is ratcheted up to the next level, no matter how much you have to go.

So, as soon as the experience starts counting up, pause the game

Do a Quick Save by hitting Up + A on Controller 2

And start a new game (or continue an old one)

You'll notice that your new Link will start to get the rest of the experience points that the old Link was going to get before you paused and exited the game!

Which is great for a few levels early on in the game.

Though this does have rather limited use. You have to actually get pretty far into the game for the amount of experience points that transfer to amount to more than a level or two for the new guy, which kind of implies that you're going to be pretty far in the game (or have finished it at least once). But if you're sharing the game with a less-skilled player, it's a good way to give him a bump up in strength to make the early going slightly easier.