Sheilda

The colloquial terms of Sheilda, Shielda, Z-Shiek, or, in official sources, Zelda/Sheik, refer to and  used in tandem via transforming in the middle of the match.

The term is usually used either out of convenience or theoretically, as mastery of two characters with differing playstyles simultaneously requires more dedication than is usually considered to be worth the effort. Furthermore, in the main series Super Smash Bros. games, it is rarely if ever used competitively due to Zelda's consistent and extreme history of disadvantages over Sheik in Super Smash Bros. Melee, Super Smash Bros. Brawl, and Project M, making Transform virtually worthless. However, in Super Smash Flash 2, both characters are viable, which in turn makes the playstyle as a whole viable.

Sheilda is currently ranked as the best character in the game. Zelda alone is considered to overwhelm most of the cast, her only poor matchups being and, which Sheik, highly competent in her own right, is able to hold her own against, nullifying those weaknesses. Furthermore, well-placed and periodic transformations allows their abilities to synergize, such as Sheik's combo potential building up damage for Zelda's early KO ability, along with the vastly different paces of their gameplay making maintaining the proper momentum against them difficult.

However, this is a theoretical ideal, albeit one with solid basis.

Match ups
As a bare minimum, due to the nature of the character, Sheilda's matchups are assumed to be the greater between the matchups of Zelda and Sheik against the given character. It is currently unknown how much the aforementioned added benefits would further skew the matchups in their favor.

Tier placement history
Sheilda's first appearance in a Super Smash Flash 2 tier list was the third and final tier list for v0.9b, where they were recognized as a separate entity for various reasons. One reason was to address concerns of character counter picking; namely, reports that players would deceptively call Sheik to influence the opponent's matchup strategy only to Transform and proceed to play as Zelda, or vice versa. Another reason was that the Super Smash Bros. Brawl tier list was a precedent; Zelda/Sheik in Brawl was considered to be marginally better than Sheik alone, ranked at number 24 as opposed to her number 25, with a larger gap between them in tier lists prior to the current one.