You can come across different looking Mountains in Creativerse. Mountain-biomes can be made of rather small Mountains consisting of grey Stone, Dirt and Grass up to large ones covered with Snow all over, with green valleys in between, and some with dark lines of Peakstone in between or on the very top. "Striped" mountains in different shades of reddish to sandy brown belong to Canyons though.
Keep an eye on the heat-scale showing up on snowy Mountains as freezing-damage over time will occur when the scale is fully filled with white color. Ice can rarely be found on Mountains, only sometimes at the entry of caves high up or in the shape of small cataracts. Also beware of Caves, as in the Mountains, a number of those have deep chasms inside that might lead to a deadly fall of careless adventurers!
Mountains are a good source of Coal and Obsidian, as you can sometimes see Nodes embedded in stone visibly on the surface/sides of Mountains. More Nodes can easily be found by digging into the Mountains (a Excavator might be of help with that).
As for animals, Rambeaus will spawn on Mountains on or close to Peakstone during the day, while blue Arctic Mirus will only spawn on Peakstone or on Snow during the night or in darkness. Also Blizzard Chizzards can spawn on Snow during the day, and Night Chizzards during the night. From Caves ordinary green Mirus, Night Pigsies and/or Night Rocksters might occasionally emerge as well.
Only a few trees will grow in Mountain-biomes, rather on the feet of Mountains and in valleys in between defined by Grass and/or Dead Grass - mainly pine-like often snow-covered Elderwood-trees with Blue Flowers on top and only rarely Beeswax in these colder climate-zones, occasionally also birch-like Ashenwood-trees, adorned with Red Flowers in their tops and Moss on their stems here or there. Red Mushrooms, Tallgrass, Turnips and/or Lettuce can only - rather rarely - be discovered in valleys or on foothills of Mountains in warmer areas.
Wood Treasure Chests can occasionally show up during (ingame-)night-times in dark places in range of view of player-characters in this biome. These rare chests can also spawn on snowy tree-tops and at cave-entrances.
Mountains can be found on ALL Creativerse-worlds, just like all the other biomes. Mind that the worlds are larger than you might initially think (10,240 x 10,240 blocks in width) and that you might have to swim across large bodies of Water (Oceans) to reach more islands/continents and to be able visit all of the existing biome-types. Keep an eye on your location by typing // in the chat: the coordinates go from +5120 to -5120 from North to South and also from East to West.