Mr. Resetti — the irate mole who confronted players who reset without saving in earlier Animal Crossing games — was removed from core gameplay in New Leaf, replaced with an optional Resetti Surveillance Centre that the player must build. If built, Resetti appears again for resets; if not built, he does not appear at all.
Visiting the Surveillance Centre after building it and speaking to Resetti’s brother Don triggers a conversation in which Don explains that Resetti was put on leave when New Leaf’s reset detection was made optional — and describes Resetti as ‘not handling it well.’ Resetti himself appears briefly in this conversation, out of uniform, and his dialogue is more subdued than any previous incarnation.
Nintendo built a transition scene for a character being made redundant by a game design change. Resetti’s entire function was to enforce saving; when Nintendo decided not to enforce saving, Resetti’s purpose dissolved. The Surveillance Centre visit acknowledges this explicitly, treating Resetti as an employee whose job was eliminated rather than a villain retired.
It is one of the more quietly melancholy things Nintendo has done: giving a notoriously frustrating character a humanising arc that only players who voluntarily built his office would see.

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.
This is the kind of discovery that keeps communities alive for years. Well documented.