Grand Arbiter Augustin IV
Legendary Creature — Human Advisor
White spells you cast cost 
less to cast.
Blue spells you cast cost less to cast.
Spells your opponents cast cost more to cast.
The Arbiter is a conduit of justice, a will so disciplined that it dispenses justice without ego or remorse.
Zoltan Boros & Gabor Szikszai
Double Masters 2022 (2X2)
• #501Rulings
This reduces only generic mana portion of mana costs. A spell you cast with mana cost {1}{W}{U} will cost {W}{U} to cast.
(wotc • 2006-05-01)
Spells you cast that are both blue and white cost {2} less to cast.
(wotc • 2006-05-01)
Rulings
This reduces only generic mana portion of mana costs. A spell you cast with mana cost {1}{W}{U} will cost {W}{U} to cast.
(wotc • 2006-05-01)
Spells you cast that are both blue and white cost {2} less to cast.
(wotc • 2006-05-01)