A Konami code variant in Castlevania has been discovered after a quarter of a century

pcgamer.com:

The Konami code is one of those Easter eggs that has long since travelled outside of its origins. It first appeared in the seminal shooter Gradius in 1986, but came to prominence in the west thanks to the NES release of Contra (it is sometimes called «the Contra code»), and basically gives the players bonuses depending on the game: in Gradius you got all the power-ups, in Contra you got 30 lives.

Funnily enough, the code was intended as a debug tool, but someone forgot to remove it and, with Gradius in the latter stages of production, the decision was made to just leave it be. Konami's developers, recognising it was hard to input accidentally but easy if you knew the secret, adopted it as something of a trademark and began including bonuses in many of its games based on the code (usually on the title screen).

The code became so ubiquitous that any new Konami game was immediately Konami-coded to oblivion by players, and it's not the most complex Easter egg, so there's been a widespread assumption that every possible use of the Konami code had been found. Not so. Two dedicated Castlevania 64 players, Moises and LiquidCat, have discovered an example that's remained hidden in Castlevania: Legacy of Darkness for 25 years (their finding was subsequently brought to wider notice by YouTuber JupiterClimb and The Gamer.) 

Castlevania: Legacy of Darkness was a quickfire 'Director's Cut' of the much-maligned Castlevania 64, Konami's first attempt to translate the 2D side-scrolling series into 3D. Castlevania 64 was infamously a technical mess but, even outside of that, simply a terrible game: even at the time it got absolutely monstered by critics and players alike. Legacy of Darkness was hastily developed and released within a year, improving the technical performance (somewhat), adding new levels and narrative beats, more playable characters, and remixing the original's locations.

I wouldn't say Legacy of Darkness is a lost classic, exactly, but it's much better than