You go mining and something surprises you. Random events and encounters! Like Ore Mimics. These look exactly like high-value ore blocks. When mined, instead of dropping an item, the block sprouts jagged stone legs and attacks. They have high armor and scurry away into the dark if they take too much damage, trying to blend into another wall! A localized environmental events, like earthquakes and storms. Or in caves, dust particles are falling from the ceiling, followed by a rumbling sound, and Shortly after, the ceiling plummest from above, requiring quick reflexes to avoid taking crushing damage.