Ok i made a priest control deck using silverfish a.i. which gave me ~61% win ratio on 14-15 ranks. I don't know if it will work for you but give it a try. I know the cards aint the best overall but as long as the results show > 50% win ratio i assume it is working good. This deck will help you survive early game and shine from mid to late. It beats most of the decks factoring the rng.

Basic concepts that the bot aims is going for juggler lightwell cleric combo buffing them with pw:shield. Disabling early threats with shadow words and also for lightspwan and divine spirit combo. In late game it goes for kelthuzad after doing argus and usually people concede when kelthuzad brings back the taunts :P It clears the board with holynova immediately also.

[ Deck ]
Circle of Healing, 1
Light of the Naaru, 1
Power Word: Shield, 2
Northshire Cleric, 2
Convert, 1
Divine Spirit, 2
Shadow Word: Pain, 1
Knife Juggler, 2
Lightwell, 2
Shadow Word: Death, 1
Thoughtsteal, 1
Defender of Argus, 2
Lightspawn, 2
Holy Nova, 2
Darkscale Healer, 2
Loatheb, 1
Holy Fire, 1
Dr. Boom, 1
Kel'Thuzad, 1
Alexstrasza, 1
Mind Control, 1

[ Tips ]
Trade Alexstrasza for another Mind Control.
Trade Dr. Boom & Kel'Thuzad for 2 x Gurubashi Berserker.

Tbh i don't recommend trades because the deck is not as efficient but for loatheb and kelthuzad you can do the naxxramas. Keep farming gold, buy the wings and win the cards. Easy. For Dr. Boom i recommend crafting it. Dust everything till you have 1600. Worth imo. For Alex just trade it with mind control if you are not lucky enough to get it in some packs. Not a big deal.

[ Settings ]
enfacehp = 15;
maxwide = 300;
twotsamount = 45;
simEnemySecondTurn = true;
playarround = false;
playaroundprob = 50;
playaroundprob2 = 70;
enemyTurnMaxWide = 20;
enemyTurnMaxWideSecondTime = 200;
enemySecondTurnMaxWide = 20;
nextTurnDeep = 6;
nextTurnMaxWide = 40;
nextTurnTotalBoards = 200;
useSecretsPlayArround = false;
alpha = 50;
simulatePlacement = true;
useExternalProcess = true;
passiveWaiting = false;
behave = control;
concedeOnBadBoard = false;
speed = true;

[ Mulligan ]
Use the default _mulligan.txt and _combo.txt files included in the silverfish.