How do you get the “welcome” badge?

What is this entity

After your done door 50 you buy it from Jeff 

After you complete the game you will get it permanently 

Go to door 100 and it’s in-front of you 

Go to door 100 and go down stairs and find it

Go to door 90 and the same thing will be there for the next 10 doors

Go to A-0000 and use the 2 lock picks then use the skeleton key