Sand Crabs are recurring enemies in the Zelda series. These aggressive land crabs are often found on the shores of lake, river, and beach.
A Link to the Past
In A Link to the Past, Sand Crabs are found in the Light World, along the shores of Lake Hylia, the Waterfall of Wishing, and the river that connects the two bodies of water. They are incredibly fast in a sideways motion, but slow when moving vertically. They are easy to defeat and can be killed with a single slash from the Fighter's Sword.
Despite appearing like relatively harmless creatures, they do a considerable amount of damage. If a crab comes into contact with Link, it will do two full hearts of damage, so be cautious when fighting these creatures.
They are also an answer for second riddle ("The scissors by the water...") in the Riddle Quest in the Game Boy Advance port of A Link to the Past.
Sand Crabs are only found on Toronbo Shores in Link's Awakening. For an enemy they're pretty basic, they just move around the screen and don't do much damage to you at all. However, since it takes two hits with your Level 1 Sword, and the fact that their movements are random, that's what makes them a somewhat difficult enemy to defeat.
Oracle of Ages
In Oracle of Ages, Sand Crabs are found around a few places in Crescent Island and they aren't too difficult at all. They randomly scuttle around at fast speeds, not provoked by them sighting you. Just run up and slash them once and it's over quickly.
Oracle of Seasons
A few Sand Crabs can be found on the Western Coast in Oracle of Seasons. Like their Link's Awakening counterparts, they just move around the screen and don't do much damage to you at all. It can be killed with a single slash.
Four Swords Adventures
In Four Swords Adventures, Sand Crabs sometimes appear on The Coast of Hyrule. In this game; they do not move vertically, but simply move left and right at high speeds. They are weak and can be destroyed easily with Sword.