Kingdom Hearts 3 provided a rousing, if bit flawed, conclusion to the Kingdom Hearts saga, but one complaint a lot of players have had with it was that it was too easy. This is partly because the base game lacks a Critical Mode, which, to be fair, previous games only got as part of their Final Mix re-releases.
But we may not have to wait till a Kingdom Hearts 3 Final Mix for a Critical mode for the game either. According to a data miner, code for the Critical Mode already exists in the game’s files. This lets you deal and take twice the damage you ordinarily would. It’s not properly implemented, doesn’t even have a name in-game, and requires a fair bit of workarounds to get it to work (and seems to be leftover code from Kingdom Hearts 0.2, actually), but there seems to be evidence that something like this is in the works. Given the scope of the game, it shouldn’t be surprising that people are finding leftover code in it, however.
If a Critical Mode is to exist, it remains to be seen how it will be added to the game—as part of a Final Mix DLC pack? A re-release? Something else entirely? Hopefully Square Enix chooses the most customer friendly option here.