Capibara

export default function (data) {

return data
.reduce((acc,el) =>{
    el.pets.map(pet => {
        if(!acc.includes(pet.name)){
            acc.push(pet.name);
        }
    })
    return acc;
},[]) //array with pets unique names
.sort()
.map(el => {
        //pets total power after each iteration
        const petTotalPower = data.reduce((acc,player) => {
            player.pets.map(pet => {
                if(pet.name === el){
                    acc += pet.power
                }
            })
            return acc;
            },0);
        //pets max power after each iteration
        const maxPetPower = data.reduce((acc,player)=>{
            player.pets.map( pet => {
                if(pet.name === el && pet.power > acc){
                    acc = pet.power
                }
            })
            return acc;
            }, 0);
        //filters the most powerful player => returns array with objects
        const mostPowerfulPlayer = data.filter(el => {
            for( let obj of el.pets){
                if (obj.power === maxPetPower){
                    return true;
                }
            }
            return false;
            })

return {
        'name': el,
        'totalPower': petTotalPower,
        'mostPowerfulPlayer': mostPowerfulPlayer[0]
        }

})

}