I am thinking of changing the 2 Kabal Songstealer for 2 Forbidden Words. But i am not sure yet.

The OTK combo that you are going for is thanks to 5 Cards. (Or 7 if you want to use the set-up as combo piece) The combo is that you pull out your Prophet Velen and use both of the 2 Mirage Caller's with reduced cost (1 Mana each) on him for 3x Times the DAMAGE on your 2 Mind Blast's with reduced cost (0 Mana each). This combo is 40 Damage total. 

The set-up is thanks you your Emperor Thaurissan together with the Drakkari Enchanter for a 2x Times card reduction.

NOTE: Dont forget to take away the enemies Secret before doing the combo so that you are not interrupted by a Secret like Ice Block, Counterspell, Eye for an Eye or Evasion. With that in mind. You can also try to reduce the cost of your friendly Eater of Secrets. And dont forget to thank him for his service :)