It turns her into a male wolf.

As the spell activated, energy filled the circle and centered on Zelda herself. Link watched in anticipation as she began to shrink, her body shifting, but to her disappointment it was clear after a few seconds she wasn't becoming an imp like herself. No, as Zelda's face elongated into a snout, her hands became paws, her breasts shrank into her chest leaving it lean and muscled, and dark twilight fur grew thickly all over her body, Link knew what her friend was becoming.

Once the transformation had finished, Link licked her lips as Zelda rose from the bed, and looked around, confused. She was a wolf now, similar to the one Link herself had become for a time. But where Link had become a grey wolf of the woods, Zelda had become a wolf of the Twilight Realm. Her fur was so dark it seemed to absorb light into itself, with the exception of the glowing sigils that branded her skin, the same as the ones on Link's own. Her eyes glowed as well, a soft blue full of confusion and fear. Lastly, and oddly, there was a large, stone disk on the flat top of Zelda's muzzle, similar in look to those on the Twilight beasts form the invasion. Link rolled her eyes, and told Zelda, "Come on, Princess, I didn't do this so you could lay around in bed!" With a snap of her fingers, Link disappeared and reappeared on Zelda's back. The feeling of the wolf's thick fur on her legs was calming somehow, and while looking around Link noticed something. "Ooh! Someone was hiding a treat!" Moving down Zelda's back, Link reached down below her legs and grabbed a long, dark wolf's cock. Licking her lips, Link said,