Hearthpwn

Shadow madness (e.g. sludge belcher) then recomboulator

it combos with Shadow Madness . if  you recomb the minion u stole. it stays with u.

Omg what pile of garbage is this?! DansGame 

totally unplayable on ladder, only for the lucky drawers...

Any replacement for ragnaros? I understand that here we are just looking for a big drop, so Maybe Kelthuzad, or Sneed old Shreder?

You typically either go with a combo of 7+ minions, the best being Dr. Boom + Rag, or all <7 attack minions, like some combination of Ysera, Sneeds, Thuzzy, and or a tech slot like TBK or Harrison.  Consider that since this deck runs recombobulator, if you recombobulate a 8/9 drop you pretty much can't go wrong (say if your Ysera is at 1 life after you hit something big, recombobulate into something like an Alexstraza).

Actually, Ragnaros is there as main threat, together with Dr. Boom. One of them baite BGH and the other do the job.

You can any big threat that you have with 7+ attack, like Mekgineer or something like that.

If you don't have any, i suggest you to play the way Penatronic told you.. With Ysera, Sneeds, Kel Thuzad (i don't like him in Priest), Mind Controls, etc..

Shadow Word: Death and Sky Piloted Golem.

As someone who plays priest on ladder, I am sorry to disappoint you, but once you understand how the deck works you can beat any deck. 

Doesn't mean the decks bad.  Priest is the hardest class by far I'm a good priest player.  But its not an easy class especially if you've never seen Amaz play it

boring.

I think maybe another 5 drop that's quite stable, maybe something like Sludge Belcher?

Another option maybe is Holy Nova if you need more removal, but I think Sludge Belcher will do just fine.

Try a second Shadow Word: Death, since Vol'jin in this deck is more a removal than a threat.

To be honest there is no replacement for voljin in a decent priest deck. he's a staple. 

I'm a legendary Priest player and I don't think that Vol'jin is that good on ladder.

Actually, the last two Priest decks that I used for legend he isn't in the list.

He's a staple on tournaments, but not in ladder, IMO.

I think this is one of the first decks I've seen without smite or SWP.