Is there an official rule or statement that Skirmishes must be played in best-of-3 Match format (rather than Duel format)?

Ruling: There is no clearly documented official statement requiring Skirmishes to be best-of-3 Match format, though it appears to be the intended design. The carde.io platform enforces Bo3 when a Summoner's Skirmish is correctly created.

Nuances:

• The organized play documentation states that matches in competitive (High OPL) must be best of 3, but can be interpreted as not explicitly requiring Match format over Duel format
• Stores reportedly received information about Skirmishes, though content and clarity varied
• Some stores are allowing players to vote on format preference