Gut ja, dann liegt eindeutig hier der Fehler... gleich der letzte Befehl der Methode.

Code: 
  def initialize
    @figure_names = ["Spinne1.png", "Spinne2.png", "Spinne3.png", "Spinne4.png", 
    "Spinne5.png",
    "Spinne6.png", "Spinne7.png", "Spinne8.png", "Spinne9.png", "Spinne10.png", 
    "Spinne11.png",
    "Spinne12.png", "Spinne13.png", "Spinne14.png", "Spinne15.png", "Spinne16.png"]
    
    @positions = [
    0, 0, 
    136, 0, 
    272, 0, 
    408, 0,
    #
    0, 104, 
    136, 104, 
    272, 104, 
    408, 104,
    #
    0, 208, 
    136, 208, 
    272, 208, 
    408, 208,
    #
    0, 312, 
    136, 312, 
    272, 312, 
    408, 312
    ]
    # number of cards horizontal
    @max_number_of_cols = 4 
    # size of cards
    @card_width = 64
    @card_height = 64
    # distance between cards
    @margin = 12
    p @positions

    @memory = Game_Memory.new
  end
Habe ich wohl etwas mal wieder falsch verstanden...

Ansonsten noch mal der ganze Code.
Code: 
class Game_Memory
  # hier kommen alle Attribute rein die dein Spiel so hat
  
  # filenames of the pictures of your cards
  attr_accessor :figure_names

  def initialize
    @figure_names = ["Spinne1.png", "Spinne2.png", "Spinne3.png", "Spinne4.png", 
    "Spinne5.png",
    "Spinne6.png", "Spinne7.png", "Spinne8.png", "Spinne9.png", "Spinne10.png", 
    "Spinne11.png",
    "Spinne12.png", "Spinne13.png", "Spinne14.png", "Spinne15.png", "Spinne16.png"]
    
    @positions = [
    0, 0, 
    136, 0, 
    272, 0, 
    408, 0,
    #
    0, 104, 
    136, 104, 
    272, 104, 
    408, 104,
    #
    0, 208, 
    136, 208, 
    272, 208, 
    408, 208,
    #
    0, 312, 
    136, 312, 
    272, 312, 
    408, 312
    ]
    # number of cards horizontal
    @max_number_of_cols = 4 
    # size of cards
    @card_width = 64
    @card_height = 64
    # distance between cards
    @margin = 12
    p @positions

    @memory = Game_Memory.new
  end

  # returns x, y coordinates as well as the image name of
  # the card with the given index
  def get_card index
    [card_x(index), card_y(index), card_image(index)]
  end

  # return all cards
  def get_cards
    # create a new array with elements
    # for all indizes from 0 upto @positions.size
    (0...@positions.size).map do |index|
      # each element contains the result value of
      # get_card
      get_card index
      end
  end
  
  # x coordinate for a given card index
  def card_x index
    col_num = index % @max_number_of_cols
    col_num * (@card_width + @margin)
  end
  
  # y coordinate for a given card index
  def card_y index
    row_num = index / @max_number_of_cols
    row_num * (@card_height+@margin)
  end
  
  # filename of card image
  def card_image index
     @figure_names[@positions[index]]
  end
  
  # number of different figures/cards
  def number_of_pictures
    @figure_names.size
  end
   
  # add 2 cards for each figure into the field
  # shuffle the positions of all cards
  def shuffle_cards
    @positions.clear
    # this loop is invoked as often as the number
    # of different cards
    number_of_pictures.times do |picture_id|
      # for each invocation, two cards are added
      # into the array 
      @positions << picture_id << picture_id
    end
    # shuffle the array at the end
    @positions.shuffle!
  end
  
end

class Game_System
  # füge Memory als Attribut hinzu
  attr_accessor :memory
end


# Erbebt von Scene_Base
class Scene_Memory < Scene_Base
  #class << self 
#-------------------------------------------------------------------------------
# Überschreibt start von Scene_Base
#-------------------------------------------------------------------------------
  def initialize_graphics
  # for each card in the game
  @card_sprites = $game_system.memory.get_cards.map do |x, y, image|
    # create a new sprite
    sprite = Sprite.new
    # set its graphic and coordinates
    sprite.bitmap = Cache.picture(image)
    sprite.x, sprite.y = x, y
    # and "return" the sprite into the array
    sprite
  end
end

def update_graphics
  # update attributes of all sprites
  @card_sprites.each_with_index do |sprite, index|
    x, y, image = $game_system.memory.get_card(index)
    sprite.bitmap = Cache.picture(image)
    sprite.x, sprite.y = x,y
  end
end

def dispose_graphics
  @card_sprites.each do |sprite|
    sprite.dispose
  end
end
  
#-------------------------------------------------------------------------------
# überschreibt  terminate Scene_Base
#-------------------------------------------------------------------------------
  def terminate
    super
    dispose_graphics
  end
  
#-------------------------------------------------------------------------------
# überschreibt update Scene_Base
#-------------------------------------------------------------------------------
  def update
    super
    update_graphics
  end
  
  def start #(start)
    super 
    initialize_graphics
    update
  end

end
#end