Hydra

Hydra is a mainly green creature type but also red used for cards that depict serpents with many heads, each of which, if cut off, grows back. The heads are mechanically represented by +1/+1 counters. Hydra is the iconic creature for the color green.

Traditionally, Hydras are water serpents, which is reflected in their name (Greek Hudra = water). In Magic they can also be associated with other environments (for example Molten Hydra). The first creature to bear the type was Rock Hydra in Alpha.

Alara
Hydras are regarded as the manifestations of the "soul of the world" of Alara, the behemoth Progenitus. Following the Sundering, Hydras were limited to the Shards of Naya and Jund. During the Conflux, new types of Hydras, like the Apocalypse Hydra, appeared that came into conflict with the other Shards, like Bant.

Feral Hydra
Unlike most Hydras, the Feral Hydra lacks any elongated necks. Their features are more feline than those of Hydras found on other planes. Their heads are known to fight among themselves about prey, tearing it apart in the process.

Amonkhet
The hydras of Amonkhet have heads like those of a cobra. Some were captured and treated as pets of the gods, while their wild cousins lived within Ramunap, hiding in the sand to wait to ambush their prey.

Dominaria
Unlike most Hydras, Dominarian Hydras are red-aligned, mostly inhabiting mountain ranges and wastelands. Molten Hydras inhabited lava, while the Balduvian Hydra was found in the steppes of Balduvia.

Eldraine
The hydras of Eldraine resemble gigantic multi-headed snapping turtles (modelled after the tarasque). They live in the untamed wilds outside the Realms and are frequent foes of questing knights.

Fiora
On Fiora, Hydras are known to have been Domesticated Hydra by the nobility of Paliano. These hydras are trained to obey their masters command, although they are difficult to train.

Innistrad
Hydras are also found on Innistrad, although they rarely come near civilization. One exemplar with five heads has been observed in the Ulvenwald. Ulvenwald Hydra heads seem to have more in common with Hellions than traditional Hydras.

Kaladesh
Kaladeshi Hydras emit the characteristic blue glow of aether from their throats. Their heads and necks are crested with barbs and Bristling Hydra. Most hydras have five or six heads, but small hydras with as few as three heads— as well as enormous specimens with eight or more — have been seen in the deep forests far from Ghirapur.

Hydras are fierce predators, favoring prey that has absorbed large quantities of aether from the environment. This taste for aether also leads them to devour aether-powered machines whenever they encounter such devices, from thopters to automatons. In the remote wilderness near Peema where hydras are plentiful, such altercations are rarely an issue. But in the rare event of a hydra coming too close to civilization — or even wandering into one of Ghirapur's greenbelts — they can cause widespread destruction in their hunt for aether.

Rath
Rathi Hydras are, like their counterparts on Dominaria, red-aligned. Examples include the four-headed Spitting Hydra</c>.

Ravnica
On Ravnica, three kinds of Hydras have been observed.

Phytohydra
Grown by the Selesnya Conclave. Carnivorous plants with hydra-like regeneration and growth abilities, they can spread at enormous speed and are depicted on cards like Phytohydra and Sprouting Phytohydra.

Simic Hydras
Created by the Simic Combine hydra mutants such as the Hydroid Krasis represent the Simics unique take upon evolution which has resulted in some of the more unique Hydras to exist in the multiverse.

Savageborn Hydra
More traditional Hydras, these entities are part of the Gruul Clans and used to unleash devastation against civilization. Once a hydra chooses a lair and declares the surrounding land its territory, it's almost impossible to drive the creature out. The Gruul revere these multiheaded predators as vestiges of the ancient times before the guilds took over the world. They don't kill hydras for trophies but pulling a spine from a hydra's neck is a mark of great bravery among the Gruul.

Shandalar
Hydras are known to live in the Kalonian Wilds. Like most Hydras, they are massive serpentine creatures with up to six heads.

Tarkir
In the old timeline of Tarkir, Hooded Hydra</c>s existed in the forests. These Hydras had strong similarities to cobras and were aligned with the Sultai Brood.

It is not known if any survived in the modern timeline.

Theros
Theran Hydras are very diverse, varying in size and their number of heads. All of them, however, have rapid regenerative properties and acidic blood. They can withstand countless attacks, and some even grow stronger if wounded but not killed. Theran Hydras lay eggs, with one of the parents hatching them. Newly hatched Hydras are already bicephalic.

Hydras can spend years dormant, but they continue to grow during this time. Great thickets grow over the largest sleeping hydras, hiding them from wanderers. When they awaken, they go on rampages that destroy great swaths of land.

Zendikar
Hydras are among the fauna of Zendikar. Relatively small hydras, such as those found in Tazeem’s Vastwood, have only five heads, but the largest hydras in Ora Ondar have eight. A hydra's heads come together on long, thin necks, connecting to a four-legged body with wide shoulders and narrow hips. Frilled crests adorn its heads and upper necks, and run down the creature's long tail. For all their great bulk, hydras can move quickly and with surprising agility through their forest homes.

Some elvish tribes are known to have made alliances with hydras, like the Khalni Hydra</c>, to protect them in times of need.

Hydra Heads
Head is a creature type that was used in the Face the Hydra Challenge Deck

Notable Hydras
Alara
 * Gyrus, a hydra of Jund with necromantic powers.
 * Progenitus, the Worldsoul of Alara.

Ikoria
 * Zaxara, a hydra from Indatha, coated in poison.

Ravnica
 * Ulasht, a hellion hydra revered by the Gruul.

Theros
 * Polukranos, a hydra slain by Elspeth Tirel . The beast is so ferocious it is said it's more an Avatar of the hydras' hunger than a normal beast, and so it will always find a way to come back and terrorize Theros, either as a zombie hydra or as a reincarnation.

Unknown
 * Gargos, Vicious Watcher</c>

Zendikar
 * Grakmaw, a powerful and extremely resilient hydra that made its lair inside one of the floating forteresses of Zendikar.

Tokens

 * Sprouting Phytohydra</c> produces tokens that are copies of the card itself.

Trivia

 * Ulasht, the Hate Seed</c> is a Hellion-Headed Hydra. The Hellion type was added later.
 * Phyrexian Hydra</c> is a Hellion-Headed Hydra, as well. The Hellion type isn't added, yet.
 * Feral Hydra</c> is a Hydra Beast.
 * Genesis Hydra</c>, Phytohydra</c> and Sprouting Phytohydra</c> are Plant Hydras.
 * Clockwork Hydra</c> is the only Artifact Hydra.
 * Aspect of Hydra</c> is an instant that pumps a creature according to its controller's devotion to green.
 * Hydra's Growth</c> is an Aura that grows a creature by doubling the number of +1/+1 counters on it.