Here's where the Surf and Waterfall HM's come in handy. There are two rooms only accessible by Surf and Waterfall, and both contain a Pokeball, though I'm not sure what is in each one. (Click the Picture to go to see what's in the cave)

Also, once you climb the nearest waterfall (once you enter) and get on the stairs to land, it seems that you will start to encounter a lot more Misdreavus (#200 Ghost). (When I was making this map I only began running into Misdreavus after going up that waterfall and onto land)