### Instruction:
What is a mulligan in Magic the Gathering?

### Response:
A mulligan in Magic the Gathering is an action you can take if you are not happy with your opening hand in a game. Depending on the format you play, different rules apply. For competitive one versus one formats, the rule is that you draw an initial hand of seven cards. If you are unhappy with the hand, you can shuffle it back in your deck, and again draw a hand of seven cards. If you are then happy with the hand, you can keep it but you have to choose and put one card from your hand and put it on the bottom of the deck. If you are unhappy, you can mulligan again, but then you'll have to put back two cards, and so forth.