[{"a":"c"},{"b":"c"},{"c":"c"},{"d":"x"},{"d":"c"},{"a":"x"},{"other_key":"c","a":"x"}]

db.collection.aggregate([{"$addFields":{"aux":{"$objectToArray":"$$ROOT"}}},{"$match":{"aux":{"$elemMatch":{"k":{"$in":["a","b","c"]},"v":"c"}}}},{"$project":{"aux":0}}])