Terrorpin

Terrorpins are turtle-like enemies found in the Palace of Darkness of A Link to the Past, in the Temple of Darkness, the Desert Temple, and Frozen Hyrule of Four Swords Adventures, and in Mutoh's Temple in Phantom Hourglass.

Characteristics
Terrorpins will slowly close in on any target in the vicinity, dishing out damage just from contact. Basic forms of attack will not have much effect on them, but a pound of Link's Magic Hammer anywhere near their standing point will cause them to flip onto their backs, revealing their weak underside and forcing them to become immobile. Their exposed belly is vulnerable to nearly any form of attack, but if they go undefeated, Terrorpins will hop onto their feet and chase after whoever humiliated them even faster. Coincidentally, a nearby hammer pound will allow them to jump back onto their feet immediately. A hammer attack directly on top of them will provide an instant kill, although this is slightly more dangerous to pull off since it requires less distance between Link and his enemy.

Four Swords Adventures adds more variety of color to the species, as well as larger versions of the foes found in the Desert Temple. At Frozen Hyrule, the Links can play a minigame called Terrorpin Hockey where they have to flip over the "Terrorpins" and hit them to make Force Gems pop out.

In Phantom Hourglass, Terrorpins, also known as Shell Spinners, attack like their previous incarnations, by spinning around and ramming into Link. Like before, they can only be defeated by slamming the ground near them with the hammer, exposing their tender under bellies. After this they can be killed by use of any weapon, though the sword or hammer are recommended.

Trivia
In terms of appearance, method of attack, and weakness, Terrorpins are very similar to Spiked Beetles and Snappers appearing later in the Zelda series. Except for the weakness, Terrorpins resemble the Heatoise mini-boss appearing in Spirit Tracks.