Talk:Shadow Stalker/@comment-72.168.145.235-20151216065132/@comment-26484802-20151216170544

He can only be fought if the Tenno has completed the The Second Dream, if the Tenno in question has not, they will be confronted with the pre-Second Dream Stalker   instead.

So i'm guessing you cant get the old stalker anymore, but if you are playing with a person who hasn't done the quest i guess.