Unless you have an immeasurable amount of heroes to spare at the Send Home page, the Arena is your main way of getting large amounts of Hero Feathers for Unlocking Potential (Fire Emblem Heroes Guide: Unlock Potential).
The Arena pits your team against other player made teams. Your opponent’s team will be controlled by AI. The level of your opponents will vary depending on the average level of your team and the difficulty you choose.
your scores are accumulated for up to 7 matches. If you win all 7 matches, your final score after the 7th match is recorded as your high score, and your current score is rest to 0. However, losing a match will also reset and record your scores, so consider carefully when choosing your opponent difficulty.
In order to earn the most point during these 7 matches, players will have to challenge harder opponents, or use a special Score Bonus Hero that increases the amount of points earned after each match.
▲Score Bonus Heroes
Players are given 3 free Duel Daggers every day, meaning they will be able to play 3 free Arena Duels every day. Dueling Daggers can be bought with orbs, or refreshed with Dueling Crests (in-game item given during special events).
Players will be rewarded in 3 separate categories: Offense, Defense and Rank. Offense is obviously the score players accumulate whilst attacking other players. Defense points is earned through successfully defending against other player’s assault (your defensive team is automatically set as the team on the furthest left in the Edit Team page).
▲Only 1 Score Bonus Hero required to gain bonus scores. Doubling Score Bonus Heroes does not increase the bonus.