Search your library for up to X basic land cards, where X is the number of different powers among creatures you control. Put those cards onto the battlefield tapped, then shuffle.
Celebrate the Harvest looks at the creatures you control as it resolves to determine how many basic lands cards you can search for. For example, if you control a 1/1 creature and a 2/1 creature at that time, there are two different powers among creatures you control.