Since the user that answered on 2023 is probably not active anymore, here goes the rules described on official Cipsoft explanation on PVP, which by the way are not Sections 5.3.4 and 5.3.5 anymore, but instead 5.3.11:
5.3.11 Player Killing
As a rule, killing other characters is legal on all game worlds of Tibia where player vs. player combat (PvP) is enabled. However, there are differences. There are no limitations on player killing at all on hardcore PvP game worlds, while there are certain restrictions on worlds with open PvP combat to make sure player killing does not get out of control. On optional PvP game worlds, player killing is only possible if both sides agreed to it.
Some general remarks:
Regardless of which game world you are playing on, you cannot deal damage to characters who have joined the same party or guild as you with the exception of friendly fire.
Characters cannot attack other players in the first 10 seconds after login, unless they are attacked and have to defend themselves.
When you attack a character (with the exception of characters with a black skull), you only deal 50% of the damage you would deal in PvE fights.
a) Ok Kills vs. Unjustified Kills vs. Assisted Kills
Some words on "justice" on worlds where a moderate amount of player killing is allowed. Of course, every automatic system has weaknesses. Players may try to abuse the protection offered by this system to provoke you in any conceivable way. Still, you should always think twice before attacking an unmarked character, no matter what he has done. You may have good excuses for attacking the character, but your fellow players may not accept them. It is not the goal of the marking rules to ensure justice but to handle most typical conflicts arising in the game in a fair and neutral way.
All your kills will be automatically evaluated and logged. As has been said before, you are free to kill as many marked characters as you like. This is because your victims have either been aggressive towards unmarked characters (white, red and black skull) or attacked you first (yellow and orange skull).
Things are different, however, with unjustified kills, i.e. kills of unmarked characters. You may only kill a limited number of unmarked characters within some limited periods of time. The marking rules on player killing are designed to penalise aggressive players. We feel it is never a good thing if you attack a character that has no mark. Therefore you have to bear the disadvantages of being marked as an aggressive player. If this does not stop you from behaving aggressively, the red skull mark comes along with the additional punishment of full item loss when dying. Furthermore, if you exceed one or more of the aforementioned kill limits, further killing of unmarked characters will mark your character with a black skull which results in even tougher sanctions.
If a kill is listed as assisted, the character has not inflicted any damage on a killed character. However, the character has helped to bring down an opponent in the last 5 minutes before the victim's death. Note that there are no assisted kills for members of your own guild during a guild war. Assisting a kill is possible in two ways, either by paralysing the victim or by being part of a trap. Trapping means that all squares around a victim are taken so that the character in the middle cannot move anymore. Being part of a trap can either be done by standing yourself on one of those fields or for example by shooting a magic wall on it. An assisted kill also counts towards the skull system, however, it will let your kill counter fill up slower than inflicting actual damage on the victim.
b) Player Killing on Hardcore PvP Game Worlds
On hardcore PvP worlds there are no restrictions whatsoever on player killing. Quite the contrary, attacking and killing other characters is actually encouraged. In addition, the spell "cancel invisibility" has a chance to destroy worn stealth rings. As you cannot walk through other characters on hardcore PvP game worlds, blocking is not rated as an attack on another character. The secure mode is always turned off on hardcore PvP game worlds and the expert mode is set to the red fist mode. Finally, harmful magic fields always deal damage to characters walking on them including the caster.
c) Player Killing on Retro Hardcore PvP Game Worlds
On retro hardcore PvP worlds there are no restrictions whatsoever on player killing. Quite the contrary, attacking and killing other characters is actually encouraged and even yields experience points if the killed character is approximately the same or a higher level. In addition, the spell "cancel invisibility" has a chance to destroy worn stealth rings. By default the secure mode is set to the red fist mode, but players can change this mode. The expert mode is not available. Finally, harmful magic fields deal damage to other characters walking on them including the caster, however, only for the first 5 seconds after creation. Also, the PvP blessing "Twist of Fate" is not available.
For more information on rules for retro hardcore PvP worlds, please take a look at the FAQ.
d) Player Killing on Open PvP Game Worlds
On open PvP game worlds a limited amount of player killing is allowed and kills are divided into 2 categories, in ok kills, i.e. kills of marked characters, and in unjustified kills, i.e. kills of unmarked characters. A character may make any number of ok kills, but too many unjustified kills within certain limited periods of time will lead to tough sanctions. For details on how characters are marked please see the next section.
Please note that a kill counts fully for a maximum of 5 characters that inflicted damage on a character in the last 5 minutes before its death. Depending on whether the killed character was marked or unmarked for them, the kill counts as unjustified or ok. If the kill was unjustified and more than 5 characters took part in the fight, the individually gained unjustified points are lower.
e) Player Killing on Optional PvP Game Worlds
On optional PvP game worlds, player killing is only possible within the scope of a guild war. Only characters who are involved in a war can attack or inflict damage on each other. Furthermore, characters cannot walk through characters and their summons with whom they are at war. Finally, a harmful magic fields does not deal any damage to the character who has cast it.
Note that neither your weapon nor your shielding skill will improve by attacking other characters or their summons during a guild war on an optional PvP game world.
f) Blocking
While you can simply walk through other characters on Optional and Open PvP game worlds, there are certain PvP situations in which characters can block other characters. Whether you will block another character depends on your expert mode settings. If the dove mode is activated, you will not block other characters at all, in the white hand mode, you will only block characters who have been aggressive against yourself or members of your party or guild. If the yellow hand mode was selected, all skulled characters are blocked. Finally, characters with the red fist mode will generally block all other characters. Of course, characters who have joined the same party or guild cannot block each other, no matter which mode you have selected.
Keep in mind that every blocking of another character is rated as an attack on this character with all negative consequences.
g) Join Aggression
To help a guild or party member in a critical situation, you can join the same fight. To do so, right-click on the other character and select from the context menu "Join Aggression". This way you are instantly transformed into the same PvP situations like the character you have joined. This means all these characters will receive damage from your area spell or be blocked from your magic wall, without the need to be aggressive with all of them beforehand. Be careful though, as this counts the same as if you had attacked every single of these characters yourself.
However, if the secure mode is active, you can only join aggression if all attacked characters fit to your predefined expert mode, i.e. all attacks on the single characters must be justified.
h) Friendly Fire
Generally, characters that have joined the same guild or party cannot block or deal damage on each other. However, there is one exception. If you and a member of your party or guild attack the same enemy combatant together, you and your guild/party ally can also block or deal damage on each other, e.g by casting an area spell. In case you manage to block or deal damage on a guild member only, you can still enter a protection zone.
