SNS - What we know so far
 

ORIGIN

Stop 'N' Swop is an idea from the very end of Banjo-Kazooie development. It was planned as feature which could allow to transfer codes between 6 games and unlock extra content. At the start there were 7 eggs but last egg was changed into ice key. Each game could unlock additional ? egg in Banjo-Kazooie and performing "full circle" (transfer with all 6 games - 6th game could send code back to B-K) could unlock ice key. SNS was planned as cold swap feature where after turning off Nintendo 64's power data can be stored in RAM for 24 seconds.

BANJO-KAZOOIE

The feature is completly coded in the game. When players found all 100 jigsaw pieces Mumbo revealed secret pictures with pink ? egg, ice key and blue ? egg and said that those secrets can be unlocked and used in Banjo-Tooie. But there are much more. Stop 'N' Swop are 6 ? eggs and ice key. Sandcastle codes to unlock them were added as backup plan if 6 games transfer plan would fail. Cold swap feature works in the game - at the boot Banjo-Kazooie is looking for extra data from another games and Banjo-Kazooie saves extra data for another games. Nintendo asked Rare to remove feature but they refused. It is fully functional in Banjo.

DONKEY KONG 64

Donkey Kong 64 was the only game outside Banjo-Kazooie where SNS was functional. Rare used ice key for connection. There could be a locked cave in Crystal Caves with lever. Pulling lever could unlock ice key in Banjo-Kazooie and then ice key could open locked cave. Diffrent ending of the game was also planned as part of feature. Nintendo seriously asked Rare to remove feature and this time they did it. Connection between B-K and DK64 was removed. Only small bits like ICE KEY 1/1 text and cutscene releated to ice key connection in Crystal Caves are left in the code.

JET FORCE GEMINI

Jet Force Gemini was planned as another game where SNS could be coded after DK64 but feature was already canned in DK64 so it was never included in JFG.

BANJO-TOOIE

SNS was already removed in DK64 so Rare included pink ? egg, ice key and blue ? egg inside Banjo-Kazooie gamepaks in Banjo-Tooie. There is also extra yellow ? egg. Those items can unlock small bonuses. SNS was never coded in Banjo-Tooie. Howewer there are a lot of mysteries in Banjo sequel...

Nice to know you're still a dedicated SNS scholar.