Stalker is an unlockable character within Call of Duty: WWIINazi Zombies, she can be unlocked by completing a full challenge set in the map The Shadowed Throne, in this case being the "Vigilant" challenge set.
Challenges
Keep Hands Clear - Handled the Stadtjäger with causion. (Heavy Machinery)
Complete Stadtjäger Down's boss fight without any player in your game going down.
Just Takes A Scratch. - Took care of a mess without incident. (I'll be Fine)
Get to Wave 31 without taking any damage from a zombie hit.
Hold Your Ground. - Banished the darkness from the depths of Berlin. (In the shadows)
Get to Wave 21 without opening any doors.
Minimalist - Rivaled the undead menace without surrendering to powers unknown. (No shiny tools)
Get to Wave 31 without any player using the Special Abilities, Mods, Consumables or Blitz Machines.
Extinguisher - Blew out the candles. (Snuff the flame)
Get 10 sniper rifle headshot kills on Gekocht zombies in a row.
