Sudden Impact deals damage to target player equal to the number of cards in that player's hand.
"Some say it's better to think before you act. While those people are considering all the options, that's usually when I kill them." —Dravus, lava mage
Each player shuffles all permanents they own into their library, then reveals that many cards from the top of their library. Each player puts all artifact, creature, and land cards revealed this way onto the battlefield, then does the same for enchantment cards, then puts all cards revealed this way that weren't put onto the battlefield on the bottom of their library.
If you would draw a card, you may instead choose land or nonland and reveal cards from the top of your library until you reveal a card of the chosen kind. Put that card into your hand and put all other cards revealed this way on the bottom of your library in any order.
Look at the top five cards of your library. You may reveal a creature card from among them and put it into your hand. Put the rest on the bottom of your library in any order.