(silly me, thinking this counted as a resource, it is more tutorial me thinks ><)
I haven't made a proper introductory post yet and, honestly, had planned to lurk as I do on most RM sites. However, it seems this little demo I made a while ago (posted at another forum) just to show how terrain tags can be used might be useful to people in this forum as well. So I thought I might contribute for once and show people how terrain tags can be used to do some neat things.
This one was a specific request, someone looking for a Pokemon Surf skill wondered how to go about making one. I only took on the travel part of it and no one ever responded for the in-battle portion. =/
It is a short demo to show how one can use Terrain Tags and switches to make certain areas passable in certain situations. There's a little flair thrown in because I can't help but add such things.
Please look throughout the Database, paying particular attention to the Tileset settings. I changed a bit in there to allow for a smoother transition of the sprite from water to land. I used invisible tiles marked as passable to get the player closer to the water before the skill can be activated, you may have other ways of doing this, but look at the options anyway. Might be useful.
Hopefully this will be useful to others, let me know if there are any questions or the demo doesn't work for some reason.
Changed Demo to executable and used map and settings from my own game testbed (meaning it includes Ccoa's UMS and rounded water).