Transform

Transform is a special move in Super Smash Bros. Melee and Super Smash Bros. Brawl. It can be used by Zelda to transform into Sheik, and the other way round by Sheik to tranform back to Zelda. The attack is good to switch between different strategies. Sheik's strength and speed can help in hand-to-hand combat, and Zelda's magic and teleportation abilities make her better at long-distance fighting, or getting back up from a fall. Using the attack at the right time, in the right situation, is hard to master.

The transformation needs a little time to complete. It can be interrupted by any regular attack.

In Super Smash Bros. Brawl, the transformation takes a conderiderably longer time to complete. Zelda and Shiek are, however, invulnerable as long as it lasts. This can be used as a way to dodge attacks like Final Smashes.

Origin
The move is based on The Legend of Zelda: Ocarina of Time where Shiek reveals to have been Zelda in disguise all along. Using the power of the Triforce of Wisdom, she is able to physically change her appearance, allowing her to disguise herself as a male. The sound that plays when Zelda/Shiek transform is the traditional Zelda "secret revealed" chime.