db={"coll1":[{"_id":0.0},{"_id":1.0},{"_id":2.0},{"_id":3.0},{"_id":4.0},{"_id":5.0},{"_id":6.0},{"_id":7.0},{"_id":8.0},{"_id":9.0}],"Dual":[{"_id":"dummy"}]}

db.coll1.aggregate([{$project:{_id:1}},{$addFields:{flag:1}},{$unionWith:{coll:"Dual",pipeline:[{$project:{_id:[5,6,"C","B"]},},{$unwind:"$_id"},{$addFields:{flag:-1}}]}},{$group:{_id:"$_id",total:{$sum:"$flag"}}},{$match:{total:-1}}])