Cheapest priced copy (Outlaws of Thunder Junction Commander): $0.49 at Card Kingdom, near mint, their price list as of .
Genesis Hydra 
Creature — Plant Hydra · 0/0 · Rare · Magic 2015 · #176
When you cast this spell, reveal the top X cards of your library. You may put a nonland permanent card with mana value X or less from among them onto the battlefield. Then shuffle the rest into your library.
This creature enters with X +1/+1 counters on it.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
8 printings · $0.49 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2020 | 172 | Rare | $0.69 | — |
| Iconic Masters | 163 | Rare | $0.69 | $2.49 |
| Magic 2015 | 176 | Rare | $0.69 | $2.49 |
| March of the Machine Commander | 298 | Rare | $0.69 | — |
| Neon Dynasty Commander | 118 | Rare | $0.59 | — |
| Outlaws of Thunder Junction Commander | 193 | Rare | $0.49 | — |
| The List | M15-176 | Rare | $0.99 | — |
| Magic 2015 Promos | 176★ | Rare | — | $1.29 |
6 rulings from Wizards of the Coast
- 17 November 2017A nonland permanent card is an artifact, creature, enchantment, or planeswalker card.
- 17 November 2017If you have fewer than X cards in your library, you reveal all of them.
- 17 November 2017If you put an Aura onto the battlefield this way, you choose what it enchants as it enters the battlefield. This doesn't target any permanent or player, but it must be able to enchant that permanent or player. For example, you could put a green Aura onto the battlefield enchanting a creature with hexproof controlled by an opponent, but not one with protection from green.
- 17 November 2017Genesis Hydra's first ability will resolve before Genesis Hydra does. Notably, if you put an Aura card onto the battlefield this way, it can't enchant Genesis Hydra.
- 17 November 2017If "the rest" is zero cards, either because X was 0 or because X was 1 and that card was put onto the battlefield, the library is still shuffled.
- 17 November 2017If a card in a player's library has {X} in its mana cost, X is considered to be 0.