Cheapest priced copy (Shards of Alara): $0.35 at Card Kingdom, near mint, their price list as of .
Sigil Blessing 
Instant · Common · Duel Decks: Knights vs. Dragons · #30
Until end of turn, target creature you control gets +3/+3 and other creatures you control get +1/+1.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Shards of Alara | 195 | Common | $0.35 | $0.49 |
| Duel Decks: Knights vs. Dragons | 30 | Common | $0.35 | — |
| Modern Masters 2015 | 187 | Uncommon | $0.35 | $0.49 |
One ruling from Wizards of the Coast
- 1 October 2008If the targeted creature becomes an illegal target by the time Sigil Blessing resolves, the entire spell won’t resolve. Your other creatures won’t get +1/+1.