Effectively doubles fall damage when landing on a dripstone (does not matter how big the dripstone is). When falling on a player after support block is removed: "the amount of damage is 1HP per pointed dripstone falling (less than 6 will be counted as 6) per each block of falling distance in Java Edition. The damage is capped at 40HP, no matter how far the stalactite falls. Wearing a helmet reduces the damage by 1/4, but this costs twice as much durability on the helmet as on other armor pieces."
Note: Each heart of a player is 2 HP
