Cheapest priced copy (Commander 2015): $0.49 at Card Kingdom, near mint, their price list as of .
Seal of the Guildpact 
Artifact · Rare · Ravnica Remastered · #266
As this artifact enters, choose two colors.
Each spell you cast costs {1} less to cast for each of the chosen colors it is.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
4 printings · $0.49 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2015 | 54 | Rare | $0.49 | — |
| Ravnica Remastered | 266 | Rare | $0.59 | $0.79 |
| Ravnica Remastered | 394 | Rare | $0.49 | $0.49 |
| Ravnica Remastered | 394z | Rare | — | — |
6 rulings from Wizards of the Coast
- 4 November 2015If a spell you cast has {X} in its mana cost, you choose the value of X before calculating the spell's total cost. For example, if that spell's mana cost is {X}{R}{G} and you've chosen red and green, you could choose 5 as the value of X and pay {3}{R}{G} to cast the spell.
- 4 November 2015If there are additional costs to cast a spell, or if the cost to cast a spell is increased by an effect (such as the one created by Thalia, Guardian of Thraben's ability), apply those increases before applying cost reductions.
- 4 November 2015Seal of the Guildpact's last ability doesn't change the mana cost or mana value of any spell. It changes only the total cost you pay.
- 4 November 2015You must choose two different colors.
- 4 November 2015The cost reduction can apply to alternative costs such as evoke costs.
- 4 November 2015Seal of the Guildpact's last ability can't reduce the amount of colored mana you pay for a spell. It reduces only the generic component of that cost.