So you're a game developer. You've spent months upon months conceptualising and refining a core vision for your game; specific mechanics, heroes and villains - but all that gets locked down fairly early on, so now what?
It's in this part of the process when things like easter eggs, secrets and references get thrown in - whether it be a coder wanting to leave their mark on a game (like Sonic the Hedgehog's hidden credits), cross-referential nods to other games and franchises, or, in this case, entire additional modes and features.
In generations past, such things would be locked away behind cheat codes, but with the rise of the internet saw the downfall of their 'worth'. Now consumers can Google the solution to any given problem or look up a specific code, rather than be forced to thumb through some magazine-attached book, hoping for the best.
Indeed, cheat codes are almost entirely out, and the age of meticulous exploration and experimentation is in. However, it's not just modern games that get picked apart to the nth degree. Many fans have retroactively pilfered their past collections, and the rewards are pretty incredible...