The Wylvan are part of the Demigoth, basically beastman races. Wylvans are a race of wolf or cat-humanoids, having some characteristics of both. This race is similar to Khajiits of the Elder Scrolls game franchise. They have a higher than average dexterity and agility. This makes them quick runners and nimble fighters. Using them for a rogue class is a good idea. They are not bad as mages either.
There are some general NPC Wylvan in the Demigoth town Skuldoon. There are also a few, but important named Wylvan:
Feros Duul- Extremely important as not only being a story quest giver, but also is a contact for the Guild of Mages. He sells almost if not all the Nether Kataals in the game.
Most enemy Wylvan appear to be at least part mage, and will attack with spells and summons rather than physical weapons.
Wylvan players can accept the Uroth blacksmith's quest available only to Demigoths.