I think that in the Dream World, you get points when you do certain actions (I forgot, go to bulbapedia and type in Dream World), but I think when you reach a certain number of points, you unlock new area, meaning new Pokemon, too. I haven't done it myself, but I read it somewhere so I'm not sure.
With your imagination in dreamland
It will be available on March 30th, i heard it was supposed to be epic.
Nara Dreamland was created in 1961.
Nara Dreamland ended in 2006.
O Dreamland was created in 1953.
The Dreamland Café was created in 1995.
Dreamland Margate was created in 1920.
Yokohama Dreamland ended in 2002.
Yokohama Dreamland was created in 1964.
Rebellion in Dreamland was created in 1995.
Dreamland Manor was created in 2005.
There are 8 worlds in Kirby's Return to Dreamland: Cookie Country, Raisin Ruins, Onion Ocean, White Wafers, Nutty Noon, Egg Engines, Dangerous Dinner, and Another Dimension.