This is how I unlocked the episodes. They're very simple to do.
You need 50 plot points each to unlock: Aliens Arrived and There was this Mummy.

I don't know whether you need to get 100% in every episode to unlock It All Came to and End.

To connect to and GBA, you need this wire thing that probably is white (it might come in other colours), you can probably buy it from your local gaming store.