Do not attack or loot other players' monsters without their permission. This includes the use of the "Greed" skill.
A monster "belongs" to another player if it is attacking, being attacked by, trapped by, or following that player.
When casting area attacks, make sure not to hit other players' monsters.
NPC_WIDECURSE, which is the skill being casted by Lich's Bone Wand, is not an attack skill, it is an area skill that inflicts a status on several monsters around you. Curse does not damage the monsters, so it's not an attack skill, which means it's not a problem according to the rules, HOWEVER, if the curse status makes the monsters that originally followed another player suddenly attack you, or if you do it deliberately by following a player and continuously bothering him with slowing his monsters, so he loses them or anything, I'd say that would warrant a punishment.
As for you demanding that we GMs do something against a certain job class frequenting this map, I'd suggest you to at first try out different places to train or collect items if you have issues with that particular map, as it seems that it's always the same people who bring foward complaints about Skellington, and I fail to see how it would be fair to ban a whole class from entering a map just because you are unable to do exactly the same as they do, albeit with a different job class.