Like we had in the Circle Tower, there are 2 ways to complete this arc, and both of them will give a different unit for the final battle.
In this video, we take the happy, good ending in it's truest form.
There is another way to get the Dalish elves to join us, but to me, it wouldn't feel right to just kill all of the werewolves without first trying to break the curse that they are desperate to be free of.
The second ending is definitely a lot darker; annihilation of the Dalish Elfs, turning those who survive into werewolves.
It does have a bit of a sad ending to it for Swiftrunner, but overall, it is definitely the bloody ending that is fun to grab if you don't like elf characters