+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.
9/20/2016 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.