I heard that there are like levels and there are rarer pokemon after each level what are they?
Pleasant Forest- After you get 7,500 points you get rarer Pokemon. Which is on the link. Also you get different items. Once you get 10,000 points you get even rarer Pokemon and Items.
You get these rarer Pokemon by getting more Dream World points. The same goes to different areas.
Windswept Sky
Sparkling Sea
Spooky Manor
Rugged Mountain