Mountain Caves

Mountain caves would be very small, like only generating a max of 40 blocks into the mountain. It would also let you find emeralds in caves again, instead of finding them outside the mountains, which is very boring. It could also be a cool starter base, allowing you to have an awesome view of the surrounding areas. A new stone called cold stone could be found in the mountains with small stalactite and stalagmite variants. A cave can also have a small lake at the end of it, with new fish that have adapted to the cold dark environments.