Grief-style playing, or griefing, is illegal. Griefing is defined by any style of play that makes the person playing a character feel genuine distress and anger through disruption of their gaming session.
Avlis is a roleplaying server. People should be in character at all times. Shouting is disabled. Using tells, IRC, and teamspeak to convey in-character information is illegal, however it is ok to use these media to talk about out of game things.
No PvP: CvC
Player vs. Player combat is illegal. However, Character vs. Character combat is LEGAL. A "player" is defined by the person sitting behind the screen playing the game. A "character" is defined by the alternate personality you portray within the game. Characters can have disagreements and fight over them, but as soon as it becomes a personal matter between the players behind the characters, it is no longer justified.
Exploitation of bugs to gain experience, wealth, or to save time is illegal and a bannable offense. This includes duplicating items and inappropriate server hopping.
Common sense is a rule. If an action goes against common sense, it's not legal.