Hydra's Growth
Enchantment — Aura
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.
Bayard Wu
Theros Beyond Death (THB)
• #172Rulings
To 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.
(wotc • 2020-01-24)
If 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.
(wotc • 2020-01-24)
Rulings
To 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.
(wotc • 2020-01-24)
If 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.
(wotc • 2020-01-24)