Board Thread:Question and Answer/@comment-26508480-20160121224747/@comment-25151790-20160122002845

After being defeated by an Archwitch that you encountered, you will see a "Reinforcements" button. Press it and select people to request assistance.

Note that you will not see the button if you are fighting someone else's Archwitch, or fighting Archwitches in the Witch Gate and Elemental Hall.

For Legendary Archwitches, assistance requests are automatically sent to the whole alliance as soon as it is encountered.