Cheapest priced copy (Jumpstart 2022): $0.35 at Card Kingdom, near mint, their price list as of .
Reckless Amplimancer 
Creature — Elf Druid · 2/2 · Common · Strixhaven: School of Mages · #141
{4}{G}: Double this creature's power and toughness until end of turn.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Jumpstart 2022 | 716 | Common | $0.35 | — |
| Foundations Jumpstart | 706 | Common | $0.35 | — |
| Strixhaven: School of Mages | 141 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 16 April 2021If a creature's power is less than 0 when it's doubled, instead that creature gets -X/-0, where X is how much less than 0 its power is. For example, if an effect has given Reckless Amplimancer -4/-0 so that it's a -2/2 creature, doubling its power and toughness gives it -2/+2, and it becomes a -4/4 creature.
- 16 April 2021If an effect instructs you to "double" a creature's power, that creature gets +X/+0, where X is its power as that effect begins to apply. The same is true for toughness.