Super Smash Bros. Melee/Sheik

Basic Techniques
Hold A after a stage has been selected (or in single player, during the matchup screen) to switch between Zelda and Sheik before the match starts.

Switching between Zelda and Sheik
An effective Zelda/Sheik game revolves around knowing when to transform. As a general rule of thumb, Sheik is better at racking up damage while Zelda provides the finishing attacks.

Advantages of Zelda

 * 1) More powerful moves, especially Smash attacks
 * 2) Great aerial attacks (particularly the lightning kick)
 * 3) Greater distance covered with Up+B and less lag
 * 4) Reflective ability (B)
 * 5) Long distance projectile (Forward+B)

Advantages of Sheik

 * 1) Quicker moves and movement
 * 2) Equally great aerial attacks (including a better-than-average sex kick)
 * 3) Better skill with melee weapons (two hits)
 * 4) Great juggling and edge guard techniques\
 * 5) More powerful Up+B
 * 6) Great attack range, particularly that of smash attacks

It is also worth noting Sheik is lighter than Zelda.