Cheapest priced copy (Shards of Alara): $0.49 at Card Kingdom, near mint, their price list as of .
Soul's Fire 
Instant · Common · Ultimate Masters · #148
Target creature you control deals damage equal to its power to any target.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
3 printings · $0.49 to $4.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Shards of Alara | 115 | Common | $0.49 | $4.99 |
| Commander Legends | 200 | Common | $0.49 | $0.79 |
| Ultimate Masters | 148 | Common | $0.49 | $0.79 |
One ruling from Wizards of the Coast
- 10 November 2020If either target is an illegal target as Soul's Fire resolves, no damage is dealt.