Cheapest priced copy (The List): $1.79 at Card Kingdom, near mint, their price list as of .
Hydra's Growth 
Enchantment — Aura · Uncommon · Theros Beyond Death · #172
Enchant creature
When this Aura enters, put a +1/+1 counter on enchanted creature.
At the beginning of your upkeep, double the number of +1/+1 counters on enchanted creature.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $1.79 to $3.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Jumpstart 2022 | 89 | Uncommon | $3.49 | — |
| The List | THB-172 | Uncommon | $1.79 | — |
| Theros Beyond Death | 172 | Uncommon | $1.79 | $2.99 |
2 rulings from Wizards of the Coast
- 24 January 2020To double the number of +1/+1 counters on a creature, put a number of +1/+1 counters on it equal to the number it already has. Other cards that interact with putting counters on it will interact with this effect accordingly.
- 24 January 2020If Hydra's Growth leaves the battlefield before its enters-the-battlefield triggered ability resolves, the creature it last enchanted before it left gets the +1/+1 counter.