I'm glad to shar my analysis of this great card. I asked myself "what is best turn to cast it, to have best chane to overhelm opponent by playing demon every turn?" My general recommendation: without coin, you should tap on turn 2 and play shadow council on turn 3. With coin, you should play shadow council on turn 2.
How to read below table
Color red example: You played shadow council on turn 1. You have 0 mana. You start turn 2 with 2 mana and 3 random demons. On turn 2 you have 64% chance that at least 1 demonis cheaper than 3 mana. You were lucky, you played demon. On turn 3 you still have 2 random demons and there is 72% chance that you can play at least one of them. On turn 4 your last random demon has 64% chance to be played. Unfortunatelly all 3 events together have only 30% to happen. (not to mention that having specific card on turn 1 is also not common).
You played shadow council on turn 2. You have 1 mana. you have 6 random demons and there 59% chance that you can play one immidietally.
So there is 50 chance % that you played random demon every turn since seond turn and 85% chane to play every turn since third turn.