ObjectManager.GetWoWUnitHostile is useful function in many cases. To select lowest HP enemy, to multi dot, etc. But useless in pvp, because returns List<WoWUnit> objects with WoWPlayer exclusion (there is woWObject.Type==WoWObjectType.Unit condition inside this function). So, proper GetWoWUnitHostile is:

public static List<WoWUnit> GetWoWPlayerHostile() {
  List<WoWUnit> result = new List<WoWUnit>();
  try {
    foreach (WoWObject woWObject in ObjectManager.ObjectList) {
      if (!woWObject.IsValid || woWObject.IsInvisible) continue;
      WoWUnit o;
      switch (woWObject.Type) {
      //case WoWObjectType.Unit:
      //  o = new WoWUnit(woWObject.GetBaseAddress);
      //  break;
      case WoWObjectType.Player:
        o = new WoWPlayer(woWObject.GetBaseAddress);
        break;
      default: continue;
      }
      if (woWObject.IsInvisible) continue;
      if (o.Reaction <= Reaction.Unfriendly && !o.IsDead) {
        result.Add(o);
      }
    }
  } catch (Exception arg) {
    Logging.WriteError("GetWoWPlayerHostile error " + arg, true);
  }
  return result;
}

public static List<WoWUnit> GetWoWUnitHostile() {
  List<WoWUnit> enemies = GetWoWPlayerHostile();
  if (enemies.Count == 0)
    enemies = ObjectManager.GetWoWUnitHostile();
  return enemies;
}

This function selects enemy players first, and if nothing found, selects hostile units.

I left some commented code in GetWoWPlayerHostile so you can see my 1st variant - 1 list with players and units together. But i think final variant is better for PVP and even for all cases

Hello, .Reaction work only on Npc, for the player check faction (o.PlayerFaction != ObjectManager.Me.PlayerFaction)