Hardcore

An opt-in status, taken one character at a time, that a single death normally ends. A hardcore character carries a yellow [HC] in front of its name, and is in one of three states: Active while it lives, Falling in the 10 minutes after a death, Fallen once the status is gone.

Fallen is permanent, and it is the status that ends, not the character: you keep playing, keep the levels and keep everything you own.

Taking it, and giving it up

You can become hardcore up to level 3, and not while you are between levels. A character above level 3 must lose levels first.

While Active you may hand the status back. You are warned first that you can only take it again at level 3 or below. While Falling you cannot hand it back, and once Fallen you cannot take it again on that character at all.

When a hardcore character dies

The moment you die the status leaves Active:

Falling, if a Pure Balm could still be used on you - see the limits below. A clock in the top-left corner counts down the time left.
Fallen, straight away, if no Pure Balm could reach you.

A kill by a DM does not count.

The window is 10 minutes from the death, and it keeps running whether or not you stay online. Inside it, only a resurrection that costs nothing restores you to Active: a Pure Balm, or any of the other free resurrections listed on Resurrection. A resurrection you pay for brings you back to life as usual, but not to Active. When the 10 minutes are up, the status is Fallen.

Deaths, level 20, level 40, taking the status and handing it back are all announced.

Pure Balm limits

A Pure Balm can only be used on a hardcore character of level 20 or above. Below level 40 a character may be saved by one; at level 40 up to five in total, counting the one already spent. The balm itself can be used once every 16 hours.

What being hardcore changes

PvP is closed between the two kinds. Outside the arena, a hardcore character cannot attack a non-hardcore one, and a non-hardcore character cannot attack a hardcore one.
The XP bank is closed to you. A withdrawal is refused; a deposit takes the experience off your character and stores nothing.
Loot and Vengeful drops come up more often in a level 40 or raid dungeon. If everyone registered in the instance is hardcore, both chances are doubled. In a mixed instance each hardcore character raises the drop chance by 20%, up to +80%, and the Vengeful chance by 10%, up to +60%. Lower-tier dungeons give no bonus.
A dungeon run is shielded from DMs. In a level 40 or raid instance holding at least one hardcore character, only an admin can teleport in.