How do i find my doppelganger someone tell me 

https://itch.io/t/1392488/good-ending

The only requirement for making peace is:  

1. Get the Soul Emblem and Flo  in the Demon City. You have to beat the two underground Dungeons first.

2. When taking the last (act5) quest of the war (after Thane got badly wounded and the fight at the tavern), make sure to visit the tavern and the bull village until you recieve the bloody /cloth.

3. Go into the hidden room of the bull-temple and enter the painting several times. You need two emblems to enter the painting and the bloody cloth to acces the important cutscene after 3 visits. In the Cutscene the MC will follow Thane to a cave.

4. You can now find the "!" new cave in the northern parts of the map. Kill the doppelganger and the war will end