In the Legend of Zelda: a Link to the Past, Link turns into a bunny upon entering the Dark World for the first time, because Link does not have the Moon Pearl. This form, which is a large pink bunny, is known as Bunny Link, and is supposedly a reflection of his innocence in this game, for the Dark World transforms the inhabitants into a form befitting their nature.

In this form, Link cannot attack, and is virtually helpless against any enemy. Once he locates and acquires the Moon Pearl, he is no longer under the effects of the Dark World, but he is still capable of being transformed into his bunny form, should he come into contact by an unknown yellow substance within dungeons. However, this revert is only temporary, and can only effect Link once.

Of note, there is no official name for this form, and is simply called Bunny Link. This site uses Link_(Rabbit_Form) for consistency with Link_(Wolf_Form) and the species tag rabbit, instead of bunny.