This is the priest deck that I took to legend this month (I scraped in with 2 hours to go!). I had a 64% win rate with my deck tracker over 64 games, but I don't track all my games as I play some on mobile.
The aim of the deck is to draw Creation Protocol and copy some of your extremely useful minions. The deck has very limited minions so you always get a decent one from Creation Protocol. Sometimes you will draw all your minions - it sucks, but you can still win.
Which minion to copy is very dependent on the match-up. Against minion aggro or tempo decks you want Ignis, the Eternal Flame. Against control you want Yogg-Saron, Unleashed or Aman'Thul. Against arcane hunter you almost certainly want Blackwater Behemoth.
Against OTK style decks (including warrior) you want Ignis, the Eternal Flame, but you will probably lose this type of match up. I think I probably only won a a couple of games against warrior. Sif mage is a bit better, but still heavily favoured towards the mage.
You almost never want to copy Ra-den unless you're well into a game with lots of minions already played (this card is usually played either as a finisher or to protect a board against a clear).
Prison of Yogg-Saron is in here 1) to reduce the number of spells, and 2) as an "oh shit" button.
The deck wins through three main routes (with a uncommon sneaky fourth one!):
1) Multiple Ignis weapons - the first is often a 1 mana poison weapons to stabilise the board. Then you want to aim for 5 or 10 mana weapons depending on board state and mana. Whether you choose to summon minions or go for health depends on the board state and match up. Against warrior you want minions from a windfury 5 mana weapon.
2) Value (Yogg and Aman'Thul) - grinding down other control decks. My experience was that I tended to beat other control decks because i) I only run a 30 card deck ii) this deck has more tempo than a typical control deck. Remeber than Aman'Thul does not kill the enemny minions - he disappears them. That means they can't ressurect them, and I won plenty of games against warlocks who didn't seem to understand this!
3) Extreme health (Behemoth) - againt hunter just out heal them. Blackwater Behemoth is excellent into ZOMBEEEES!!! and I won plenty games through this interaction. Worth noting is that Blackwater Behemoth will attack the mininon summoned by Hidden Meaning (assuming the secret was played first). I was very sceptical, but Twilight Torrent is also decent in this match up.
4) There is a fourth (very unrealiable win con) which is to resummon and copy discovered charge minions with Ra-den and Aman'Thul. Usually you kill your own Ra-den then use the summoned Aman'Thul to copy the re-summoned charge minions. This also works with Dar'Khan Drathir.
Deck strategy is to keep Creation Protocol and any discover effects. Against aggro or paladin you probably want a board clear too. Against Rogue you want a silence (probably Shard of the Naaru). Never keep a minion - we want to discover them, not draw them. Ignis is the most versatile minion so you never want to draw him naturally. Power Chord: Synchronize can also give you your opponents win-con and is especially good with multiple Dar'Khan Drathir being resummoned by Ra-den.
In terms of substitutes I don't think there are any substitutes for the minions. You probably don't need Ra-den but adding another spell reduces the chance you find Creation Protocol with Thrive in the Shadows.
I tried using the locations to reduce the number of spells, but it's probably not as good. With the locations I also tried Dispossessed Soul and this was OK, but it does reduce the consistency of the hit with Creation Protocol. Maybe a deck without Ra-den could try it? Fan Club is lackluster in this deck and Cathedral of Atonement has too few targets and you nearly always have quite a full hand. I also tried Dirty Rat to increase the win-rate against warrior, but again, on balance, it loses more games than it wins. I didn't try the priest weapon, but this seems like it would be objectively worse than the locations. I also tried a version using love everlasting and Identity Theft but it struggled against any early focussed decks.
It is (imo) a fun deck, and no two games play out the same way. Just a shame that Odyn, Prime Designate is in the game. That said, my final "boss" was against a warrior, and playing Odyn, Prime Designate cost them the game...karma I guess!