Jace's Sanctum
Enchantment
Instant and sorcery spells you cast cost 
less to cast.
Whenever you cast an instant or sorcery spell, scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)
Illustrated by
Magic Origins#61RareEnglishLegality
Rulings
Jun 22, 2015
The first ability of Jace’s Sanctum can’t reduce the colored mana requirement of an instant or sorcery spell.
Jun 22, 2015
If there are additional costs to cast an instant or sorcery spell, apply those before applying cost reductions.
Jun 22, 2015
Jace’s Sanctum can reduce alternative costs such as miracle or overload costs.
Jun 22, 2015
Jace’s Sanctum’s scry ability will resolve before the instant or sorcery spell that caused it to trigger.