The Wind Waker
GameBoy Advance Connectivity
One of The Wind Waker's brand new features is the possibility to connect the GameCube to the GameBoy Advance using a specific cable. By doing so, a second player will be able to take part in the adventure as Tingle, and help Link throughout his quest.
Once Link has found the appropriate item in The Wind Waker, he will be able to communicate with Tingle. At this moment, the player handling the GBA (without any game in the slot) will see a map pop up with Link represented by an arrow and the enemies by dots. The hidden places will also be revealed to him. He will also be able to intervene by throwing bombs and by showing Link those hidden places.
Even if this connection between the two consoles isn't necessary at all in order to finish the game, it should be useful enough and bring even more fun to it!