-Hardcore difficulty shares the same difficulty parameters as Hard mode.

-You cant press escape or enter while outside of the main menu while hardcore is active. You can still close the game window, though.

-The level select in the extras carries over the difficulty you selected.

-The achievement you get for beating hardcore mode is "Lucifus Cake".

(I know there are still some lingering bugs in the game, but I cannot patch them currently due to my still broken pc atm. Also be aware that the next few patches I can hopefully make in the future are hypothetically going to be the last v1 patches, as I'm not too happy with how hard/hardcore mode turned out. Make of that what you will.)

(Also, be sure to press f in the game over screen lol.)