Cheapest priced copy (Core Set 2021): $0.35 at Card Kingdom, near mint, their price list as of .
Rookie Mistake 
Instant · Common · Core Set 2021 · #66
Until end of turn, target creature gets +0/+2 and another target creature gets -2/-0.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Core Set 2021 | 66 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 23 June 2020You can't cast Rookie Mistake unless you choose two creatures as targets.
- 23 June 2020If one target creature becomes an illegal target before Rookie Mistake resolves, the other is affected as appropriate.