If you would lose the game due to having 0 or less life, instead you don't and your life total becomes 20.

Each player begins the game with Sovereign's Realm in their Command Zone

If you break a rule, you lose.

All players share a deck and a graveyard. You own every card you draw for purposes of things like Homeward Path.

You must play every card in your hand as soon as legally possible.

All optional modes are mandatory, to the extent that you can fulfill them (ex. casting Mnemonic Wall with an empty graveyard is legal, but if there’s any spells in the yard you must target one with Mnemonic Wall’s ETB trigger).

You must activate every activated ability of permanents you control once per turn per legal target as soon as legally possible.

You must attack with all legal attackers and block with all legal blockers whenever the option is presented to you.