var Ninja = new Class({
  Extends: Human,
  Implements: [Warrior],
  initialize: function(side, name, age){
    this.side = side;
    this.parent(name, age);
  }
});

var blackNinja = new Ninja('evil', 'Nin Tendo', 'unknown');
blackNinja.eat(); // inherited from Human
blackNinja.attack(bob); // copied from Warrior
bob.isAlive; // false, bob never had a chance
blackNinja.kills; // 1, from Warrior