Ancient god inheritance.
When does Wang lin fuse both of his bodies ? What kind of powerup did he get ?
edited November 2016
Well, for the Gu (Ancient) body and Immortal he fuse and separate several times in the novel. However, all of this is temporary so basically the fuse is just the Gu become the body and the immortal become qi cultivation making him can burst power higher than his cultivation realm.
It is not a problem now since Wang Lin isn't pure Gu or pure immortal but it is later revealed when he got golden immortal blood (pure immortal blood) from Lian Daofei (who is direct descendant of Immortal Ancestor) that Gu(ancient) and Immortal power reject each other, it is can be traced back to the time of Gu Zu (Ancient Ancestor) and Xian Zu (Immortal Ancestor).
He will also got Gu Zu blood and soul blood and part of Immortal Ancestor inheritance
It is not until he is at Xian city that he got help from Gu Dao and he manage to initiate a permanent fusion of Gu and Immortal power (initiated, to completely fused he need more time). He also has origin/source/dao essences true body and clone born in nothingness
when he fused all of his origin true body he appeared in Heaven treading bridge which signifying him exceeded Da Tian Zun level (in issth this should be peak Dao realm paragon level but I'm not really sure) although he only manage to tread until the third bridges. For the clone born in nothingness, he was at the 7 bridges level at this point and it help him tread further (just like Gu Zu and Immortal Ancestor only they are not using clone but they are born in nothingness) and speed up the fusion of Ancient and Immortal power