Weres of the North
Baring-Gould (who was very well-read in Scandinavian sagas) identifies some common features of Norse were-wolves, were-bears, etc.:
1. In beast form their strength was thought to be multiplied by 2 or 4, or else was thought to be a sum of their normal human strength plus the animal’s normal strength.
2. They can always be recognized, in beast form, by their eyes, which appear as their normal human eyes.
3. There were three distinct kinds of shape-changers.
3.1. Some simply donned a belt of animal hide or a cloak or tunic of animal fur/feathers and were transformed. This would include swan-mays and some berserkers. (This theme would later develop into stories of belts made of human skin, or salves given to witches by the Devil.)
3.2. Some went into a cataleptic state while their spirits inhabited an animal such as bear, bird, etc. One warlock inhabited a whale. Odin often did the same thing, inhabiting animals and humans, male or female. Finnish and Lapp (Sami) witches were thought to be especially good at this. (This sounds like something you’d see described by shamans.)
3.3. Some transformations were simply illusion spells, and one might turn into a beast or even inanimate objects. Other magic-users could detect this, but normal people would be fooled.
It probably goes without saying that the main weres in Nordic legend were were-bears and were-wolves, but we should also count swan-mays (women who turn into swans using a coat of feathers; they are sometimes identified with Valkyries too), were-bulls (one hero’s spirit went into a great bull that slew foes during a battle), were-falcons and -eagles (sorcerers and the gods favor these forms), and the aforementioned were-whale. A whale with human eyes should creep the hell out of a party of adventurers whether they are on a small skiff or a longboat.