Heres a guide to Vol.2's Doppelganger, in which you need to fight at least twice in order to get all of its items. Heres the key steps:
0. Import saved data from Vol.1 containing The Own King key item, then finish Vol. 2.
1. Go to Ѳ Forgotten Deity's Moonlight.
2. Either find and kick Sleipnir/or fill your morale gauge.
3. Drive into Doppelganger after finding him.
4. Use the Sleipnir trick like Vol. 1/or use your awakening to obliterate its health. (I used Demon Awakening)
5. Finish the fight and area, then leave.
6. Come back to this area or another fielded area with Moonlights keyword and fight a 2nd time.
Thank you for watchin/reading this. Im definetly not the best when it comes to these things but I have fun doin them. I hope you found this Guide insightful or amusin.
The Atoli pic used this time came from here: https://dav-19.deviantart.com/art/Chibi-hack-190854957
All rights belong to their respected owners. Farewell and have a good one.
