Akhlut
The ferocious Akhlut comes to us from the folklore of the Yupik people indigenous to western, southwestern, and south central Alaska and far eastern Russia. This bizarre beast is said to be a spirit that can appear as an orca or a wolf, but is at its deadliest when it appears as a hybrid of the two. It has a ravenous hunger that it is not afraid to slake on any human caught unawares.
One of the more popular myths of the creature's origin is that the Akhlut was born out of a man's obsession with the sea. This man was so enthralled with the ocean that it provoked a peculiar change in him. After spending so much time in his beloved body of water, he was unrecognizable to the people of his village; they exiled him, and he took to roaming the wild. The man discovered a pack of wolves, and out of desperate hunger transformed into one to join their hunt. But he could not resist his love of the ocean, and this longing drove him to return to the water. When he jumped into the sea, he transformed into an orca, finding that he was capable of becoming both wolf and killer whale. Now he is a killer spirit that roams the arctic; he mostly swims in the ocean that has so enamored him, but will occasionally transform into a wolf or wolf-orca hybrid to seek revenge on land against the people who forsook him.
Some scholars postulate that the arctic wolf's occasional willingness to swim may have contributed to belief in the Akhlut; perhaps the Yupik saw wolf tracks leading to and from the ocean, and surmised that the likeliest explanation involved a shapeshifting spirit. The arctic environment is deadly, and there is plenty of room for a belief in dangerous spirits to arise in order to help explain the harsh environment. But others argue this is a condescending attitude to take towards indigenous people, and that they likely would be aware of the behavior of the animals that shared their land. In any case, the best advice available under the circumstances is to avoid arctic areas showing wolf tracks, and if those tracks lead to the ocean, then it's best to be wary of any ocean-dwelling dangers lurking nearby--such as the Akhlut.