Hardcore

Hardcore mode is a game mode variant of survival, differing primarily by the lack of the ability to respawn (instead, the world is deleted) and change difficulty. The mode was introduced in Beta 1.9 Pre-release 2 and officially added in Minecraft 1.0. The idea came to Notch from a Minecraft gameplay blog on the PC Gamer site.

Features
While playing hardcore mode, the game is set to “hardcore” difficulty, which only differs from “hard” difficulty in that it cannot be changed to another difficulty while playing the world. As of Minecraft 1.3, the Bonus Chest and Cheats options cannot be enabled in Hardcore mode. If the player dies, the world is deleted and the player is taken to the title screen. In the world selection screen, it will say that the world is in hardcore mode in bold, red letters, as a warning.

When the player dies, the game over screen only offers a button to delete the world save instead of survival mode’s and  buttons. The world save still exists until the button is pressed, leaving the opportunity for one to keep their world by using 3rd party tools. Exiting the client and loading the world again only reloads the game at the game over screen.

Multiplayer
Hardcore Mode has been made an option for multiplayer, and its functions are similar (and now that Single Player runs on a multiplayer database, it is VERY similar now. :D). Dying while in the server does not give the player a respawn button, replaced with a button prompting the player to "Leave Server". When clicked, the player gets the message "You have died. Game over man, it's game over!", as well as: Banned from server" "Reason: Death on hardcore". If you try to reconnect to the server, it says "You are banned from this server!".

However it is possible for players to join back into the server they died from. The server admin has to stop the server and go into the server files. Deleting the player data from (Map name)> players > (deadplayer).dat As well as going into the banned-players.txt and erasing any data under the index( banned by | banned until | reason) can un-ban players. The admin can then start the server and they can spawn again. Doing this will cause the player to enter under the original spawn point and have no items, armor, levels or effect due to the deleting of the .dat file.

Trivia

 * While playing hardcore mode, the heart icons of the life gauge are different, as they show two small blood vessels (or eyes).
 * In the world selection screen, Hardcore mode is written in red and says "Hardcore mode!"
 * When a world in hardcore mode is created with the Beta 1.9 pre-release, then played with the Beta 1.8 version, the world is permanently converted into a standard survival world.
 * When Notch announced hardcore mode on Twitter, he jokingly posted an image of an "Ultra Hardcore" mode where the premium status of the player's user account is revoked on death.
 * It is actually possible to respawn in hardcore mode, via defeating the Ender Dragon and activating the credits, after which you will promptly respawn, without world deletion or death.
 * Many Minecraft enthusiasts played hardcore mode before the official version was released. It was simply on the honor system to delete your world if you died. This was often called an "Ironman" game.
 * Via hacking, it is possible to play a cross between hardcore and creative mode. The player can fly and place infinite blocks like in creative mode, but the world will be deleted upon death. This is because there are separate variables determining if creative, survival or hardcore is on.
 * A simple way to access creative mode while in hardcore mode is to go to the pause screen and select "Open to LAN", and click "Enable Cheats". Then use any command you wish. (I use this all the time xD)