Before i start,i would like to apologize if make a spelling or grammar mistake as i am not a native english speaker.
This deck have quite a lot of winning condition. You can still win the game if you are missing some of the cards.
The Ultimate Combo: Malygos + Prophet Velen + Flash Healx2 + Light of the Naaru + Mind Blastx2 + [card]Auchenai Soulpriest[/card] = 96 damage (10 mana)
Above combo is hard to pull to off and very unrealistic. But you can win just by using few of the cards. Below is the example of some of the combo that you could pull off.
Combo 1 : Prophet Velen + Flash Healx2 + Mind Blastx2 + [card]Auchenai Soulpriest[/card] = 40 damage (6 mana)
Combo 2 : Prophet Velen + Malygos + Flash Heal + Light of the Naaru + [card]Auchenai Soulpriest[/card] = 36 damage (5 Mana) Thanks to Pewpewblast for discovering this.
Combo 3 : Prophet Velen + Malygos + Mind Blastx2 = 40 damage (6 mana)
Combo 4: Alexstrasza + Malygos +Flash Healx2 + [card]Auchenai Soulpriest[/card] = 35 damage[15 from Alexstrasza] (5 mana)
Combo 5: Alexstrasza + Malygos + Prophet Velen + Mind Blast = 35 Damage[15 from Alexstrasza] (5 mana)
Mulligan : Any card for above combo are worth keeping. Also keep any card that can draw a card for combo with Chromaggus . Chromaggus into Power Word: Shield or Azure Drake are very strong.
Card Choice :
Malygos : The main reason that i added this card is because of extra combo potential. Sometime you might not draw into Prophet Velen or [card]Auchenai Soulpriest[/card]. This card can help you win the game.
Card replacement suggestion:
If you had any suggestions or questions, please write it in the comment below. I will try to answer it the best i can . Thank for enjoying the deck.