The copy - hand-made by Gory Detail's Chris Seavor, the man behind Conker's Bad Fur Day - will be the only one "in the entire universe".
The puzzle itself hasn't been decided yet, but it's likely that it will form part of the game's title screen, which features sliding mechanical titles that open up and reveal the various options and game modes. Seavor is reluctant to reveal too much more, as he says it will be "too much of a clue as to where to look", but he will admit that it won't be easy to crack.
Both Seavor and fellow Gory Detail founder Shawn Pile have said they will also investigate means of ensuring that the person who solves the puzzle has legitimately purchased a copy of the game, rather than downloading a pirated version (lest we forget Rusty Pup is also coming to iOS devices).
Don't forget to check out the full devlog here.