Tips

Facts that are true, easy to miss, and cost something when you do not know them. Each one is explained in full on the page it links to.

Dying

Below level 5 a death costs no experience at all, and below level 40 you can never lose a level: the overflow becomes a debt instead. Resurrection
You keep your equipment when you die. What falls on the ground is another player's corpse you were carrying, and anything you stole. Death
Only a party member can raise you. Being in a party with the people you are adventuring alongside is what makes a corpse recoverable. Parties
A god catches you sometimes - but only if you have a deity at all. A character without one is never caught. Death

Gems and tokens belong to the account, not the character, and so does the vault. A gem picked up by one character is usable by every other. Sockets, Tokens
A 24-hour listing on the trade post is free. The fee only starts at 48 hours, and it is charged when the item sells, not when it is listed. Trade post
All the copies of one gem share a single socket. Sockets
Banking experience costs a quarter of it. Vault

A party spread more than eight levels apart earns nothing - and so does one whose average has fallen 4.5 below its highest member. Parties
To be paid for a kill you must be within 50 metres of it and alive. Parties
A dungeon instance can only be destroyed in the first five minutes, before anything has happened in it. Dungeons
A raid boss goes berserk twenty minutes in. Bosses

Nobody can attack you until you have both marked each other as enemies. PvP
In a Battle Royale you may carry anything in, but only item level 16 and below can be worn or used inside. Battlegrounds