So, for
Spreading Plague, I was wondering why the wording of it was so different than other "summon a minion" for each enemy minion cards (Unleash the Hounds, Protect the King).
This one is basically "Cast this spell once for each enemy minion" where the spell summons a 1/5 taunt scarab.
So, your opponent has 7 minions on board and you cast it into your empty board. The spell is cast 7 times. Does this reduce your Arcane Giants by 7 mana? Does it count as 7 spells cast for Yogg?
If you have Gadgetzan Auctioneer down and you cast it and your opponent has 7 minions, do you draw 6 cards?
IMO, as printed, it would seem like the answer to all of the above would be yes. And there's probably other synergy cards with spell casting I'm overlooking (Red Mana Wyrm?)
Edit: Trump is reviewing this card live now. I will add any of his comments related to the above.