+3: You gain 3 life.
−4: Reveal the top two cards of your library. Put all land cards from among them onto the battlefield and the rest into your hand.
−12: Creatures you control get +5/+5 and gain trample until end of turn.
The set of creatures affected by Nissa's last ability is determined as the ability resolves. Creatures you begin to control later in the turn and noncreature permanents that become creatures later in the turn won't get +5/+5 or gain trample.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.