Mountainous worlds contain common resources found on many other types of worlds. They are, not surprisingly, peaked and rich in stone and rock. They are also home to several interesting sub-biomes such as mountain healing springs. By most standards, these worlds are not much harsher than forests and jungles. They are notably the best source of valuable Zerchesium Ore.
While they contain few real threats, they may be dangerous to new players, and traversing them without a grappling hook and/or pulse jump can be tedious.
Mountains themselves are rich in mineral, densely-studded with ore veins and hollowed out caves whose walls can hold even more minerals. Some of these caverns can be surprisingly large with steep drops - those without fall damage mitigation should exercise particular caution when jumping off edges or mining directly downwards.
Note: Mountainous planets can be found orbiting Red, Blue and Frozen Stars.
Tips
There are many things that partially/completely protect you from fall damage. These include, but most likely not limited to:
While it is probably fairly obvious by the name, these worlds are rather bumpy and mountainy. They are rich in resources and quite difficult to explore without climbing gear.
Variants
Mountainous planets are not all the same. Their surface biome has 4 variants: Mountainous (see below), Mountainous II, Mountainous III and Mountainous IV. They have different blocks and monsters (including bees).
Details
Name: Mountainous
Tier: 3 - 4.4
Found around stars: Temperate Star, Radioactive Star, Frozen Star, Fiery Star, Binary Star, Red Star, Blue Star