Classic was a sanctioned casual Magic Online format that allowed all sets and cards (including promotional cards). The format was introduced to be an alternative to the Vintage format. It was retired on June 12 2014, when Vintage was introduced to Magic Online.
Normal deckbuilding rules do apply: decks must be a minimum of 60 cards and contain no more than 4 copies of any card, excluding basic lands, Relentless Rats, and Shadowborn Apostle.
The following cards are restricted in Classic Online tournaments: