This hostile crab has dripstone spikes growing upwards from its shell and it spawns in dripstone caves. It’s about one block across and moves by scuttling along sideways and climbing up walls and along ceilings, rotating appropriately.
Where possible, it prefers to be on the ceiling, where it knocks down dripstone spikes to land on the player. The fallen spikes don’t drop items, and the broken ones grow back to their previous length much, much faster than usual to prevent it from griefing the world, even if the dripstone spike wouldn’t normally be able to grow (what’s going on behind the scenes is that the dripstone isn’t actually destroyed, only made temporarily invisible and intangible while a clone falls downwards).
When on the ground it attacks with its pincers.
It’s drops include dripstone spikes, crab meat (which can be cooked and eaten for medium hunger but good saturation), and, occasionally, one of it’s claws.
If the player acquires two claws and holds one in each hand, they can climb up most flat walls. If the player only has one claw in use they remains hanging in place until they choose to fall off or equip a second claw. The claws lose durability while in use.
In a unique case, two claws with different durabilities that are otherwise identical (same name, enchantments, etc.) can be stacked in a single inventory slot. This is just to prevent clutter because you do need two to climb.