Ditto match
A ditto match or a mirror 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.
Strategies
Strategies for a ditto match often vary greatly from the character's normal strategy. An example would be a Marth ditto match; as both players have access to Marth's long, far-reaching sword, neither player receives an advantage, as well as making approaching considerably more difficult. Another example would be in a Super Smash Bros. Captain Falcon ditto match; due to Captain Falcon's incredible combo ability and his propensity to getting combo'd, the match ends up taking advantage of player flaws more frequently than usual.
A general strategy is to be unpredictable at all times and use experience with a character (knowing combos or recovery strategies) against the other player. Snake is a good example of this; in a mirror match of the two, the players have to use projectiles in such ways to make the stage difficult to navigate.
