Cheapest priced copy (Kamigawa: Neon Dynasty): $0.35 at Card Kingdom, near mint, their price list as of .
Regent's Authority 
Instant · Common · Kamigawa: Neon Dynasty · #32
Target creature gets +2/+2 until end of turn. If it's an enchantment creature or legendary creature, instead put a +1/+1 counter on it and it gets +1/+1 until end of turn.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Kamigawa: Neon Dynasty | 32 | Common | $0.35 | $0.49 |
One ruling from Wizards of the Coast
- 18 February 2022If it is both an enchantment creature and a legendary creature, you still only put one +1/+1 counter on it and it gets +1/+1 until end of turn.