In this Magic The Gathering format, all cards must have been printed at common rarity in a set or product. Common promo cards are only legal if the card meets that qualification.
If a common version of a particular card was ever released on Magic the Gathering, any version of that card is legal in this format.
Other than that, the usual rules for constructed decks apply:
Minimum of 60 cards in the main deck
(There is no maximum size for main decks)
Up to 15 cards in your sideboard, if used
No more than 4 of any individual card in the main deck and sideboard combined (with the exception of basic lands)
The following cards are banned in this format:
Cloud of Faeries
Empty the Warrens