Cheapest priced copy (Foundations): $0.49 at Card Kingdom, near mint, their price list as of .
Primal Might 
Sorcery · Rare · Foundations · #766
Target creature you control gets +X/+X until end of turn. Then it fights up to one target creature you don't control. (Each deals damage equal to its power to the other.)
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
10 printings · $0.49 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Foundations | 643 | Rare | $0.49 | — |
| Foundations | 766 | Rare | — | — |
| Core Set 2021 | 197 | Rare | $0.49 | $0.79 |
| Core Set 2021 | 377 | Rare | $1.49 | $2.49 |
| Breaking News | 32 | Rare | $0.49 | $0.99 |
| Core Set 2021 Promos | 197p | Rare | $0.59 | $1.99 |
| Core Set 2021 Promos | 197s | Rare | — | $1.79 |
| Starter Commander Decks | 204 | Rare | $0.49 | — |
| Secret Lair Countdown | 73 | Rare | — | — |
| Secrets of Strixhaven Commander | 283 | Rare | $0.49 | — |
4 rulings from Wizards of the Coast
- 23 June 2020If the creature you control is an illegal target as Primal Might tries to resolve, no creature gets +X/+X. If that creature is a legal target but the creature you don't control isn't, it still gets +X/+X.
- 23 June 2020If you choose two target creatures and either target is an illegal target as Primal Might tries to resolve, neither creature will deal or be dealt damage.
- 23 June 2020You can cast Primal Might targeting only the creature you control.
- 23 June 2020You can cast Primal Might with 0 as the value of X to just have the two target creatures fight.