How do you get missigno? And where is the cinnamon island?
Upstairs, in the last door on the left, you can enter codes. Entering one will take you to Cinnamon Island, and there you can find Missingno. You can find the code by defeating a trainer that appears after talking to a lady, who tells you "Joe found a bug." If I remember the name correctly. It's random and it's not always there.