What you need:
A Basic understanding of mapping in RMXP
RMXP(duh.)
Obviously, make a new map with the mountain tileset, You will see this.
Start off by making a jagged rock facing at the bottom, like this:
You have to remember, there is no straight lines in nature.After that make a stream and a rock facing that looks like this:
I would have given you a screenshot of the process, but I messed up
Anyways, go to layer 2 and start on some of the plants and trees and add the bridge, but don't go overboard on the trees, we need some space for the hard part!
Now, go to layer 3 and finish the bridge rails, and if you like, overlap some trees to give it a cool effect.
Now for the hard part. Make two or more rock facings in the blanks you left in the trees.
Remember, no straight lines in nature!!Now that you are done wth that, finish up the mountainy feel by adding some more foliage such as flowers, more trees, and possibly a spring and then you have your mountain!
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Tips
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You might improve your bridge by adding some river Sound effects, it works like this:
Play BGS: '010-River01'. 80. 100.