This aims to improve minecraft cave generation through the addition of a few new structures, 6 new ores, and 13 new underground cave biomes, many of which can be combined to form combo caves which can bring the count to above 30 caves.
Mycelium Cave [Removed in 1.1 due to it crashing the game for an unknown reason]
Pine Moss Caves
Different caves can be found at different y levels and some can be found in different biomes.
While making this mod I watched videos featuring ideas for a minecraft cave update. Some ideas have been borrowed from those videos. You will be able to find most of them just by searching up "Cave update ideas" on youtube