The Slayer special property will increase the damage dealt to a specific creature type. In general this is more useful to mages, especially when it is a quest weapon with stats inferior to tinkered loot weapons. (By using the quest weapon, a melee/archer is usually giving up the chance to use armor rend or critical strike and so gains little, whereas the mage gets essentially a double vuln). If you are looking for all items that have a particular slayer property, see here.
Wands may have both the Maelstrom of Souls Gem and a slayer (Mukkir or Undead). Whichever is added last is the icon that will display on the wand and the wand will be attuned to the person that added the last item (even if the item was attuned to someone else who added the first item).