Terrorpin

Turtles (also known as Pometto) are an enemies found exclusively in the Palace of Darkness of A Link to the Past. These monsters 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, Turtles 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.

Trivia

 * In terms of appearance and weakness, Turtles are very similar to Spiked Beetles appearing later in the Zelda series.
 * Another turtle-like enemy appears in  Majora's Mask, the Snapper. Both have the belly as their weak point, and so must be defeated in a similar manner.