Banjo-Kazooie’s Stop ‘N’ Swop — the mystery of six ice eggs and a key in unreachable portions of the original game — was intended to connect with Banjo-Tooie through a save transfer mechanic. The Nintendo 64’s memory system would allow data from the first game’s cartridge to influence the second game. The mechanic was removed late in Kazooie’s development due to hardware concerns about the cartridge-swap process damaging memory.
Tooie still acknowledges Stop ‘N’ Swop — there are chambers in the game designed to receive the Stop ‘N’ Swop items, and placeholder rewards were built — but the actual transfer was impossible on the original hardware. The chambers are accessible through the Ice Key and eggs, but obtaining them on N64 required cheat codes.
In 2008, the Xbox Live Arcade versions of both games added a software implementation: completing Kazooie on XBLA allowed transferring the Stop ‘N’ Swop items to Tooie, unlocking the chambers properly. Ten years after the mechanic was first teased, players received the actual intended experience.
The Stop ‘N’ Swop story is gaming’s longest gap between intended feature and functional delivery.
Stumbled across this on a late-night session and couldn’t believe it. Your explanation finally made it click.
The attention to detail the developers put into this is insane. Most players will never see it but it makes the world feel so much richer.