[rgss]class Interpreter
  ##
  # Battler id (-1 returned when not in battle)
  #
  def get_battler_id(variable=id)
    unless $game_temp.in_battle
      return $game_variables[variable] = -1
    end
    $game_variables[variable] = $scene.get_active_battler_id
    return
  end
 
  ##
  # Battler id (-1 returned when not in battle)
  #
  def get_battler_index(variable=id)
    unless $game_temp.in_battle
      return $game_variables[variable] = -1
    end
    $game_variables[variable] = $scene.get_active_battler_index
    return
  end
 
  ##
  # Battler enemy? (Return false when not in battle)
  #
  def is_battler_enemy?(switch=id)
    unless $game_temp.in_battle
      $game_switches[switch] = false
      return true
    end
    $game_switches[switch] = $scene.instance_eval("@active_battler.is_a?(Game_Enemy)")
    return true
  end
end
 
class Scene_Battle
  ##
  # Return the index of the current active battler. (-1 with no active battler)
  #
  def get_active_battler_id
    unless @active_battler.nil?
      return @active_battler.id
    end
    return -1
  end
 
  ##
  # Return the index of the current active battler. (-1 with no active battler)
  #
  def get_active_battler_index
    unless @active_battler.nil?
      return @active_battler.index
    end
    return -1
  end
end
[/rgss]

You can then use a script call where you call the methods. It could for example be:
[rgss]get_battler_id(2)
get_battler_index(3)
is_battler_enemy?(1)
[/rgss]

get_battler_id(2) will set variable 2 to be the id of the battler. (The one they have in the database) this is the one you'll want.
get_battler_index(3) will set variable 3 to the index of the battler. If Arshes is the left-most hero then the index will be 0, then 1, then 2, etc.
is_battler_enemy?(1) will set switch 1 to ON if the battler is an enemy and OFF otherwise.

When I talk about battler I talk about the one who triggered common event. I.e. the one doing the skill.