Unlike heroes Shamans have two form of growth stages and levels so unless you increase the stage you will get stuck in a level. So all the Shamans with exception of Baggi you need to purchase the packs in order to get them and grow them.

Einar the Free is for Siege strength (And it is not free).

Wendla of Shadow is for your scouts and spying.

Inga the Wise helps with Knowledge and Troop Training.

Baggi the Big helps with Construction and Production.

I am sure there will be more Shamans introduced as we are missing one for Cavalry and Killers. As soon as you build the Hall of Mysteries you are granted your first and free Shaman: Baggi the Big. Each account after level 12 can build the Hall of Mysteries and the Rune Workshop. You can switch between Shamans for free without using gold as you do with heroes but you manually changed their gear unlike herosets. Shamans like heroes add capabilities, have gear and added benefits. A the end of 2017 Plarium introduced Shamans to the Game of Vikings War of Clans.

Vikings war of clans hero