Every time KS'ing or Griefing ismentioned, it becomes a hot debate.
Some feel it just good old fun, others feel its ok due to no PVP, and still others feel that it hinders their game playing fun. It is sometimes very hard to figure out, due to general lag, invisible mobs and players, and even view distance settings. So, let me define what I mean exactly by Killstealing and Griefing.
Killstealing:
Targeting mobs already ingaged by another player on purpose with the intent of taking the mob from the previous player.
Griefing:
Willfully hindering the game play of another player by action, including spawn hogging, dragging mobs to players with the intent of getting them killed by the mobs, or any action that interfears with anothers normal game play.
One thing we see in Horizons is Spawn hogging. Because of multiclassing and the skills it provides a player, some have the ability to gather up all the mobs in a spawn area, and with little danger, drag them away to be killed. If nobdy else is in the same spawn area, this really is no problem. But when ever a spawn area is already occupied, and others come along and run in to do this, it can be considered both Killstealing and griefing. Both kinds of conduct are against the EULA.
Sadly, some who have done this, feel it is their right as a multiclassed player to do this. They express justification that others not as capable have less right to be at the spawn than them.
Some feel that it is great fun to do these things. Some feel that it's one way to get back at "enemy" players since there is no PvP. These justifications are always one sided when it occurs, and never satisfy the ones griefed by such actions.
So, what can be done?
First off, since such conduct is against the EULA, submit a ticket with any screen shots and copies of logs the tell the tail.
Second, don't decend to the same level as the griefers. If your response is filled with anger over this obviously unfair situation, then things will often get out of hand, and you might find yourself doing exactly what you are accusing them of doing. Responding with abusive words rarely works to defuse any ugly situation, and lowers you to the same level. Calmly explain that you were here already and that there is plenty mobs to go around. If this leads to abusive comments from the griefers, then its a good time to realize that talking may not solve this problem.
Reemeber, you have choices.
Even though it is NOT fair that you move to another spawn, if you move and they don't follow you, then the problem is solved for now. If however, they decide to follow you around to continue their brand of "fun" what can you do?
One method is to call a few friends, and just stay put. Be VERY careful with this method. It is very easy to fall into doing exactly what you are upset about. Patiently wait to pull mobs that are obviously not tagged by the problem group. Make NO taunts or threats. Quietly and calmly fill the spawn area with too many players. Soon there will not be enough mobs to support the players or the griefers. They will hopefully become bored with the lack of opportunity and move elsewhere. Remember, mobs belong to everyone, including those that may seek to hinder your gaming. They have no more "right" to the mobs than you.
TG wants us to try to work out player to player issues between ourselves. And generally, the issues must be harmful before they will become involved. There is no established method to lodge a complain against another player besides what I listed as the first step. However, we all realize that if a player is seen by a large part of the shard as KS'ing, Griefing, or being abusive it will become known. No need to lower yourself and announce it in market place. Just have a ton of your friends come out and quietly watch what is happening. Let peer pressure and being observed alone embarrass them. IF they stubbornly continue to do this, no matter. Soon, and without overt action, the shard will become aware and respond for you.