Very, very strong deck I came up with against this tough NPC.
Darkscale (2-8-4-7) is essential to the strategy, to barely capture his Nael (when it's below), potentially capture a Yutsuyu east, while still being weak enough so that you can recapture it from the west with an 8.
Any decent legendary card should work; I preferred something with a 9 or higher North-facing, so that you can potentially capture Yotsuyu if needed.

I even made an imgur album with pics at the time :D
https://imgur.com/a/tAufE1o

1. You play Estinien at Southwest
2. He caps it with Nael from the South
3. You cap his Nael with a Darkscale at Mid
4. He often caps your Darkscale with something from North
5. now you play your Phoebad at West and recap the Darkscale.
Most games will go like this, and you're in a winning position