Database
[{hero__marvel__avangers:{name:"Iron Man"},hero__marvel__xmen:{name:"X Man"},hhero__dc__justic_leage:{name:"Bat man"}}]
Query
db.collection.aggregate([{$addFields:{array:{$filter:{input:{$objectToArray:"$$ROOT"},as:"item",cond:{$regexMatch:{input:"$$item.k",regex:".*marvel.*",options:"i"}}}}}},{$replaceRoot:{newRoot:{$arrayToObject:"$array"}}}])