Ditto match
A Ditto Match is a match where both players choose the same character. They are different from other matches in that neither player has a match-up or stage advantage over the other player. The name comes from the definition of 'ditto', which means 'the same'. Ditto matches occur at times during tournaments. Another common term for a ditto match is a mirror match.
Strategies
Strategies for a ditto match often varies greatly from the character's normal strategy. This is especially the case for characters such as Marth or Jigglypuff, whose strategies rely on an advantage in range, mobility, or attack speed. This variation is removed during a ditto match. Another example would be smash 64 in falcon dittos where even low ranked falcons can take off top people due to incredibly easy combos (similarly, Jiggylpuff dittos and rest) and yoshi dittos where DJC'ing isn't as common.