Cheapest priced copy (Modern Masters 2015): $0.99 at Card Kingdom, near mint, their price list as of .
Apocalypse Hydra 
Creature — Hydra · 0/0 · Rare · Modern Masters 2015 · #171
This creature enters with X +1/+1 counters on it. If X is 5 or more, it enters with an additional X +1/+1 counters on it.
{1}{R}, Remove a +1/+1 counter from this creature: It deals 1 damage to any target.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
3 printings · $0.99 to $8.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Battlebond | 217 | Rare | $1.29 | $2.49 |
| Conflux | 98 | Mythic | $1.29 | $8.99 |
| Modern Masters 2015 | 171 | Rare | $0.99 | $1.49 |
2 rulings from Wizards of the Coast
- 1 February 2009The first ability checks the number you chose for X, not the amount of mana you actually spent.
- 1 February 2009For example, if X is 4, Apocalypse Hydra enters with four +1/+1 counters on it, but if X is 5, it enters with ten +1/+1 counters on it.