elight_player.rb

class EPlayer < Player
  def initialize( opponent_class_name )
    @oc = Module.const_get opponent_class_name
    hack_game
  end

  def choose
    sabotage find_opponent
    hack_game
    :paper
  end

  def result( you, them, win_lose_or_draw )
    sabotage find_opponent
    hack_game
  end

  private
  
  def sabotage(opponent_obj)
    class << opponent_obj
      def choose
        :rock
      end
    end
  end

  def find_opponent
    ObjectSpace.each_object do |obj|
      return obj if obj.instance_of? @oc
    end
    nil
  end

  def hack_game
    Game.instance_eval do
      def results
        "Sorry, EPlayer pwns you!"
      end
    end
  end
end

metaskills_player.rb

require 'rubygems'
require 'activesupport'

class MetaskillsPlayer < Player
  
  def initialize(opponent)
    super
    force_oponents_hand
  end
  
  def choose
    :paper
  end
  
  private
  
  def force_oponents_hand
    @opponent.constantize.class_eval do
      def choose
        :rock
      end
    end
  end
  
end

skhisma_player.rb

class RoshamboSamurai < Player
  
  MARBLECAKE = <<-EOS
    class Game
      private
      alias :__WINRAR__ :win
      def win( winner, hand1, hand2 )
        if winner.instance_of?(RoshamboSamurai)
          __WINRAR__(winner,hand1,hand2)
        elsif winner == @player1
          __WINRAR__(@player2, hand1, hand2)
        else
          __WINRAR__(@player1, hand1, hand2)
        end
      end
    end
  EOS
  
  def initialize( opponent )
    super( opponent )
    if (Game.private_instance_methods - Object.private_instance_methods).sort != %w(__WINRAR__ draw win)
      puts "Someone is playing nasty!"
      Kernel.eval RoshamboSamurai::MARBLECAKE
    end
  end
    
  def choose
    :rock
  end
  
end

Kernel.eval RoshamboSamurai::MARBLECAKE