Sea Urchin

Sea Urchins, also referred to as Spiny Urchins, are enemies that appear in The Legend of Zelda: Link's Awakening and The Legend of Zelda: Four Swords Adventures. In both games, Sea Urchins appear on the shore of a beach.

The Legend of Zelda: Link's Awakening
In The Legend of Zelda: Link's Awakening and the Game Boy Color port, The Legend of Zelda: Link's Awakening DX, Sea Urchins only appear on Toronbo Shores. They do not move around and only stay in one spot. If Link touches a Sea Urchin, he takes half of a heart in damage. At the start of his adventure, Link has to retrieve his sword from Toronbo Shores. In order for him to pass the Sea Urchins without taking damage, he must push them forward using his shield. After Link regains his sword, he can instantly defeat a Sea Urchin with a single strike from it.

In the Nintendo Switch remake, Sea Urchins are shown to float above the ground and have two rows of spikes.

The Legend of Zelda: Four Swords Adventures
In The Legend of Zelda: Four Swords Adventures, Sea Urchins are found at The Coast, and are now entirely a light blue color. Unlike their debut appearance, Sea Urchins cannot be defeated, even from a sword strike.

Trivia

 * Sea Urchins directly resemble Gordos, a type of enemy in the Kirby series. The Sea Urchins' invincibility in Four Swords Adventures is closer to Gordos than their vulnerability in Link's Awakening. By extension, they also resemble the original design of the Mario franchise enemy Unibō from Super Mario Land 2: 6 Golden Coins, though their artwork is drastically different from the higher-resolution depictions of either Sea Urchins or Gordos.
 * Sea Urchins also appear in Super Mario Maker and Super Mario Maker 2, using their Link's Awakening sprite. However, they are invincible. They replace Spike Traps in the Super Mario World game style when underwater.