If anyone needs help with the final boss, here is what you have to do.
1. NEVER go into the pink areas of the map. That includes the top of the mountain. You will auto lose.
2. Defend like normal until reinforcements arrive.
3. After the guy arrives, click and drag him to the top of the pink mountain. Have your archer summon wait at the map's bottom and climb the other mountain that has no pink on it to easier defend and guide the guy.
4. When he reaches the top, a cutscene will play. After this happens, resummon the archer to the pink mountain's top as well.
(This took way too long to figure out)
((If anyone has a save from before this fight starts I would appreciate it. Thanks.))