World generation

Hello! i am trying to create a world that uses elements found in games like starbound or terraria. Using a method i think is called Perlin noise i have made a script that generates a surface for the world.

The perlin script basicly creates a set of graphs with a x value that increases by 1 for every reference point (where actual terrain is going to spawn) and a random y value (float) between 0 and 4. When adding these graphs together you get a nice surface to the world.

My question is if anyone has any tips on how higher terrain should be spawned (like mountains / cliffs)? Having terrain only between the y values 0 and 4 will get pretty repetitive after a while. I have a few things in mind, like if every reference point has a 1 percent chance of spawning a mountain with a random height and width.

If anyone knows about a smart method id be more than happy to hear it!

Thank you