Solution

1. The "X" is directly behind you at the beginning of the Beach Stage

2. Cave:When you see the three fake Bulbasaur look on the wall opposite of them

3. Tunnel:To the left of the door that is next to power generator the Zapdos zaps

4. Cave: After you pass Jynx look down and behind you before you pass into the Jigglypuff stage area a frozen waterfall will be visible below you

5. River: Psyduck

6. Rainbow Cloud: The  "ground"

7. Valley: The swirling pool that Staryu flies into and Dragonite comes out of

8. Tunnel: Directly behind you when you start

9. Volcano: Rapidash at beginning

10. Tunnel: Kakuna