Wolfos
The Wolfos (ウルフォス, Urufosu) is a wolf-like enemy that appears in The Legend of Zelda: Ocarina of Time and The Legend of Zelda: Majora's Mask. In Ocarina of Time, they appear in the Sacred Forest Meadow, the Forest Temple, the Spirit Temple and Ganon's Castle. In Majora's Mask, they appear near the Southern Swamp, and replace the White Wolfos of Snowhead after Snowhead has been defrosted.
A Wolfos can be a difficult enemy to beat if you're not used to hard fighting. The best strategy is to Z-Target it and use the shield constantly, then attack when it drops its guard (try to wait until it spins and its back is exposed - if you strike the tail, it will be defeated instantly). Another way to beat it is to use the Hookshot or a Deku Nut to freeze it, then attack at will.