Assisting is a mechanism in the game whereby one can request help from a friend. The friend's first maiden will replace the member of one's attack crew with the lowest level. One can request assistance as many times as they wish, but only once per friend every 8 hours. Assists are sorted by the number of times one has personally requested help from that friend.
A common strategy used by even the top players is to leave one pixie with cost of 1 in their ATK crew, as it will be replaced with the assist and cost minimal. Furthermore, while using this strategy, players can remove and re-add the same people to their friends list, as this resets the 8 hour wait time. Although time consuming and tedious, it is effective.