I have been thinking of a way to make Harbinger Celestia useful and I see potential in her effect.
The way to win is use Emperor Thaurissan and Drakkari Enchanter to reduce your deck cost by 2. Then you play Harbinger and Treachery her. In the next turn, you can play Unlicensed Apothecary->Brann Bronzebeard-> 2x Corpse Raiser->Treachery your Unlicensed Apothecary-> Sacrifical Pact the Unlicensed Apothecary with Deathrattle.
The deck showcase is here folks, special thanks to Mr. GerritDeMan for recording the video.
Smooooooooooth 55 damage to op face. Bam Bam Bam!
Wonderful art deserves a wonderful deck!
I suggest you to replace Mal'Ganis with Violet Illusionist if you don't have dust. I put 1 Dreadlord and 1 U.Apothecary out for 2 Kobold Librarian for drawing and because we need only one U.A for the combo. Thank you for all the upvotes, I will update the video soon. ^^
I added a Loot Hoarder and a Bloodmage Thalnos for card draw efficient. How is your experience with Harbinger now?
I added the video that my friend helped me to record. He suggests me to replace Loot Hoarder with Zola the Gorgon for the hand not to be full and Zola also provides another Emperor Thaurissan in a turn. Thank you guys again for all the upvotes.