Rampant Rejuvenator enters the battlefield with two +1/+1 counters on it.
When Rampant Rejuvenator dies, search your library for up to X basic land cards, where X is Rampant Rejuvenator's power, put them onto the battlefield, then shuffle.
Use Rampant Rejuvenator's power as it last existed on the battlefield to determine the value of X for its last ability.