Jace's Sanctum
Enchantment
Instant and sorcery spells you cast cost 
less to cast.
Whenever you cast an instant or sorcery spell, scry 1.
"For all our lofty talk of keeping watch, we had no idea what we were getting into." —Jace Beleren
Adam Paquette
Commander 2019 (C19)
• #88Rulings
The first ability of Jace’s Sanctum can’t reduce the colored mana requirement of an instant or sorcery spell.
(wotc • 2015-06-22)
Jace’s Sanctum’s scry ability will resolve before the instant or sorcery spell that caused it to trigger.
(wotc • 2015-06-22)
If there are additional costs to cast an instant or sorcery spell, apply those before applying cost reductions.
(wotc • 2015-06-22)
Jace’s Sanctum can reduce alternative costs such as miracle or overload costs.
(wotc • 2015-06-22)
Rulings
The first ability of Jace’s Sanctum can’t reduce the colored mana requirement of an instant or sorcery spell.
(wotc • 2015-06-22)
Jace’s Sanctum’s scry ability will resolve before the instant or sorcery spell that caused it to trigger.
(wotc • 2015-06-22)
If there are additional costs to cast an instant or sorcery spell, apply those before applying cost reductions.
(wotc • 2015-06-22)
Jace’s Sanctum can reduce alternative costs such as miracle or overload costs.
(wotc • 2015-06-22)