[Scripting Question] Trying to create sand footprints

[Seenit45]

I'm currently trying to change the script for Essentials 21.1 so that characters can leave footprints while walking on sand. The way it works is that, whenever a character moves to a new tile, the script activates an animation from the database (like the grass rustle animation, for example) that plays on the tile that the character was previously on. This method works well for the player, but the issue is with the npcs. If I load up my save state and I have an NPC who:

• is on same map that I am
• was initially placed on a sand tile and is constantly moving

the game will immediately crash while trying to play the footprint animation.

This is the code that I made for the sand footprints animation

def triggerLeaveTile #This function already existed within Essentials, but I added the "if" with leaveFootstep
    if @oldX && @oldY && @oldMap &&
       (@oldX != self.x || @oldY != self.y || @oldMap != self.map.map_id)
      EventHandlers.trigger(:on_leave_tile, self, @oldMap, @oldX, @oldY)
      if $map_factory.getTerrainTagFromCoords(self.map.map_id, @oldX, @oldY, true).shows_sand_step
        leaveFootstep
      end
    end
    @oldX = self.x
    @oldY = self.y
    @oldMap = self.map.map_id
  end
  
  def leaveFootstep #This is the function that I made (@stepshape is initially = 0)
    if @stepshape == 1
      @stepshape = 0
    else
      @stepshape = 1
    end
    if (@oldX && @oldY)
      spriteset = $scene.spriteset(map_id)
      if (@oldX == self.x && @oldY != self.y)
        spriteset&.addUserAnimation(8 + @stepshape, @oldX, @oldY, true, 1)
      elsif (@oldX != self.x && @oldY == self.y)
        spriteset&.addUserAnimation(10 + @stepshape, @oldX, @oldY, true, 1)
      end
    end
  end

And this is the error message I get when I load up my savestate:

Exception: NoMethodError
Message: undefined method `spriteset' for #<Scene_DebugIntro>

Backtrace:
Game_Character:410:in `leaveFootstep'
Game_Character:395:in `triggerLeaveTile'
Game_Character:421:in `increase_steps'
Game_Character:584:in `move_generic'
Game_Character:591:in `move_down'
Game_Character:770:in `move_forward'
Game_Character:430:in `move_type_random'
Game_Character:950:in `update_command_new'
Game_Character:943:in `update_command'
Game_Character:927:in `update'

Can anyone help me understand what went wrong? I saw other functions within the [[ Game Clases ]] section of the script use "spriteset = $scene.spriteset(map_id)" and they don't cause the game to crash, so I'm kind of at a loss here.