Cheapest priced copy (Throne of Eldraine): $0.35 at Card Kingdom, near mint, their price list as of .
Joust 
Sorcery · Uncommon · Throne of Eldraine · #129
Choose target creature you control and target creature you don't control. The creature you control gets +2/+1 until end of turn if it's a Knight. Then those creatures fight each other. (Each deals damage equal to its power to the other.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Throne of Eldraine | 129 | Uncommon | $0.35 | $0.49 |
4 rulings from Wizards of the Coast
- 4 October 2019If the creature you control is an illegal target as Joust tries to resolve, no creature gets +2/+1. If that creature is a legal target but the creature you don't control isn't, it still gets +2/+1 until end of turn if it's a Knight.
- 4 October 2019You can't cast Joust unless you choose both a creature you control and a creature you don't control as targets.
- 4 October 2019The target creature you control gets +2/+1 only if it's a Knight as Joust resolves. It'll still fight if it doesn't get +2/+1.
- 4 October 2019If either target is an illegal target as Joust tries to resolve, neither creature will deal or be dealt damage.