Newly released card sets become tournament legal for sanctioned, rated tournaments on the following dates:
|• Hour of Devastation™
||July 14, 2017
||September 29, 2017
|• Rivals of Ixalan™
||January 19, 2018
Cards from Prerelease tournaments, spoiler cards, and cards stolen from Wizards of the Coast headquarters in grand heists are not legal for use in tournaments until the set they are from is officially released. This list is constantly updating, and we’d be surprised if the MTR is the first place you go to look for these dates.
For official Prerelease tournaments only, new sets are legal for use before the official format legal date. In these cases, any announced rules updates shall be in effect at these tournaments, including informal explanations of new rules and mechanics. Judges may apply additional rules that they believe will be updated.
This is the one obvious exception. Prerelease tournaments are treated as though the set was already released. Any changes to the rule, whether big or small, are in effect at the Prerelease tournament even though they aren’t officially brought into effect until the release of the set. Judges applying rules they believe will be updated should be incredibly obvious rules additions, such as allowing masterpieces to be played without a legal magic border.
These dates may be subject to change. Any changes will be announced at http://www.magicthegathering.com.
This clause is unlikely to ever be relevant, but it’s here in case it’s ever needed.