its been a very long time since i made a post but just wanted to say i fucking called it  So in the most recent chapter 390, it was revealed that Silver was actually Gray's father, sorta.
So basically Silver is just a corpse that Deliora took over which makes sense seeing as Gray recognised he wasn't the same person, but it got me thinking. All the back when Silver was first introduced in chapter 353, he's seen to be visiting a grave after he had frozen the sun village as he thought Atlas was a demon, does seem a bit odd that a demon who was just living in a dead man's body to kill other demons and mourn for people via visiting their graves. Also its kinda weird that a demon would have devil slayer magic. Hopefully these aren't just plot holes but something bigger, just a speculation but perhaps when Deliora possessed Silver's corpse it inherited his memories and in way Gray's father was revived and perhaps we'll see an inner conflict between Silver and Deliora.
Just on an ending note and further speculation in chapter 368, it's seen that Silver recognises who Natsu is and perhaps that means that Natsu has an essential role to play in the revival of E.N.D (evil natsu dragneel?), which seems pretty plausible as Zeref revealed that he has known Natsu for a long time. Hopefully we'll get a badass fight next chapter and some awesome FairyTail action