db.users.update(
  {
    'purchased.plan.dateCreated':{$gte:new Date('2014-02-22'),$lt:new Date('2014-02-29')},
    'items.gear.owned.armor_mystery_201402':null,
    'items.gear.owned.head_mystery_201402': null,
    'items.gear.owned.back_mystery_201402': null,
    'purchased.plan.mysteryItems':{$nin:['armor_mystery_201402','head_mystery_201402','back_mystery_201402']}
  },
  //{_id:1,'purchased.plan':1,'items.gear.owned':1}
  {$push: {'purchased.plan.mysteryItems':{$each:['armor_mystery_201402','head_mystery_201402','back_mystery_201402']}}},
  {multi:true}
)/*.forEach(function(user){
    printjson(user);
  });*/