The cost reduction applies only to generic mana in the total cost of spells you cast with the permission granted by Urianger Augurelt's last ability
Even if youre not really sure which cards are better or worse, looking at this layout of cards can help you figure out some to cut just by aiming to keep each pile balanced, perhaps with a bit of favoritism for creature cards over non-creatures and cheaper cards over expensive ones
So, if you have just quested with a character, you can take out an opponent's character with Pyros and immediately ready the card you just exerted
As for what exactly will be different about Whispers in the Well other than the cards it will introduce, the expansion will bring a mechanic called Whispers to the TCG
3/2 Illustrated by David Rapoza Standard Not Legal Alchemy Not Legal Pioneer Not Legal Historic Not Legal Modern Not Legal Brawl Not Legal Legacy Legal Comp
Are you building a new Bombadil deck