[{"matches":[{"secondParticipant":{"name":"Maria","battlesWon":2},"firstParticipant":{"name":"Fabio","battlesWon":1},"duelId":"6c3e532d-3c0e-4438-8289-c86a4a51a102",},{"secondParticipant":{"name":"Fabio","battlesWon":1},"firstParticipant":{"name":"Maria","battlesWon":1},"duelId":"6c3e532d-3c0e-4438-8289-c86a4a51a102"},{"secondParticipant":{"name":"Luiz","battlesWon":1},"firstParticipant":{"name":"Jose","battlesWon":1},"duelId":"6c3e532d-3c0e-4438-8289-c86a4a51a666"}]}]

db.collection.aggregate([{"$unwind":"$matches"},{"$addFields":{"matches.participants":[{"k":"$matches.firstParticipant.name","v":"$matches.firstParticipant.battlesWon"},{"k":"$matches.secondParticipant.name","v":"$matches.secondParticipant.battlesWon"}]}},{"$unwind":"$matches.participants"},{"$group":{"_id":{duel:"$matches.duelId",name:"$matches.participants.k"},"matches":{"$push":{duelId:"$matches.duelId",firstParticipant:"$matches.firstParticipant",secondParticipant:"$matches.secondParticipant"}},score:{$sum:"$matches.participants.v"}}},{"$group":{"_id":"$_id.duel","matches":{"$first":"$matches"},"score":{$push:{k:"$_id.name",v:"$score"}}}},{"$addFields":{"score":{"$arrayToObject":"$score"}}}])