gistfile1.rb

class Player
  @stairs = false
  @wall = false

  def play_turn(warrior)
    if damaged_from_behind(warrior)
      warrior.shoot!(:backward)
    else
      if first_non_empty(warrior.look) == "enemy"
        warrior.shoot!
      else
        if warrior.feel.enemy?
           warrior.attack!
        elsif warrior.feel.captive?
          warrior.rescue!
        else
          if warrior.health < 20
            injured(warrior)
          else
            explore(warrior)
          end
        end
      end
    end
    @health = warrior.health
  end
  
  def can_fight?(warrior)
    warrior.health > 15
  end
  
  def taking_damage?(warrior)
    warrior.health < @health
  end
  
  def injured(warrior)
    if taking_damage?(warrior)
      if can_fight?(warrior)
        warrior.walk!
      else
        warrior.walk!(:backward)
      end
    else
      warrior.rest!
    end
  end
  
  def explore(warrior)
    if warrior.feel.stairs?
      @stairs = true
      if @wall
        warrior.walk!
      else
        warrior.pivot!
      end
    elsif warrior.feel.wall?
      @wall = true
      warrior.pivot!
    else
      warrior.walk!
    end
  end
  
  def first_non_empty(spaces)
    first_non_empty = "blank"
    spaces.each do |space|
      if space.enemy?
        return "enemy"
      elsif space.captive?
        return "captive"
      end
    end
    return first_non_empty
  end
  
  def damaged_from_behind(warrior)
    warrior.health < 20 && taking_damage?(warrior) && first_non_empty(warrior.look(:backward)) == "enemy"
  end
  
end

The main other thing I'd note is usually when I write something that ends up with a bunch of if, else, elsif blocks in it I usually try to go back and refactor it into some smaller methods. Like in the play_turn method I could see having helper methods you could call for should_shoot, should_attack, and check_health each of which would only have a single if statement. Not a big deal but might make for a little cleaner code.

I use the @stairs and @Wall instance variables to make sure I've explored all spaces so there is no captive remaining.

I've updated the code: https://gist.github.com/nicusg/6290804