Coming July 5th: A Very British Mulligan
Starting July 5th, with the launch of Magic: The Gathering Core 2020 (AKA M20), a new Mulligan rule comes into affect. This changes the way you draw a new hand when you're not happy with the one you have at the beginning of the game. This is called a mulligan, which means "do-over".
The new mulligan rule is:
103.4. Each player draws a number of cards equal to their starting hand size, which is normally seven. (Some effects can modify a player's starting hand size.) A player who is dissatisfied with their initial hand may take a mulligan. First, the starting player declares whether they will take a mulligan. Then each other player in turn order does the same. Once each player has made a declaration, all players who decided to take mulligans do so at the same time. To take a mulligan, a player shuffles the cards in their hand back into their library, draws a new hand of cards equal to their starting hand size, then puts a number of those cards equal to the number of times that player has taken a mulligan on the bottom of their library in any order. Once a player chooses not to take a mulligan, the remaining cards become that player's opening hand, and that player may not take any further mulligans. This process is then repeated until no player takes a mulligan. A player can take mulligans until their opening hand would be zero cards.
For more information on this new Mulligan and what it could mean for you, check out this article from Wizards.