[{"_id":"608642db80a36336946620aa","title":"titleHere","types":{"flashcardReversed":[{"normal":{"_id":"608d5b290e635ece6828141X","front":"2front","back":"2back"},"reversed":{"_id":"608t5b290e635ece6828141Y","front":"2frontReversed","back":"2backReversed"}},{"normal":{"_id":"608a5b31a3f9806de253726X","front":"2front2","back":"2back2"},"reversed":{"_id":"608a5b31a3f9806de253726Y","front":"2frontReversed2","back":"2backReversed2"}}]}}]

db.collection.aggregate([/** pipeline two*/{"$unwind":"$types.flashcardReversed"/** get each object inside flashcard*/},{"$group":{/** run on each object $unwind returns*/"_id":{card:{"_id":"$types.flashcardReversed.normal._id",front:"$types.flashcardReversed.normal.front",back:"$types.flashcardReversed.normal.back"},card2:{"_id":"$types.flashcardReversed.reversed._id",front:"$types.flashcardReversed.reversed.front",back:"$types.flashcardReversed.reversed.back"}}}}])