Wren's Run Hydra

Reach
This creature enters with X +1/+1 counters on it.
Reinforce X—{X}{G}{G} ({X}{G}{G}, Discard this card: Put X +1/+1 counters on target creature.)

Hunting Wilds

Kicker {3}{G} (You may pay an additional {3}{G} as you cast this spell.)
Search your library for up to two Forest cards, put them onto the battlefield tapped, then shuffle.
If this spell was kicked, untap all Forests put onto the battlefield this way. They become 3/3 green creatures with haste that are still lands.

Aspect of Hydra

Target creature gets +X/+X until end of turn, where X is your devotion to green. (Each {G} in the mana costs of permanents you control counts toward your devotion to green.)

Stream of Life

Massive Might

Target creature gets +2/+2 and gains trample until end of turn.

Mistcutter Hydra

This spell can't be countered.
Haste, protection from blue
This creature enters with X +1/+1 counters on it.

Ironscale Hydra

If a creature would deal combat damage to this creature, prevent that damage and put a +1/+1 counter on this creature.

Penumbra Wurm

Trample
When this creature dies, create a 6/6 black Wurm creature token with trample.

Forest

Wild Growth

Enchant land
Whenever enchanted land is tapped for mana, its controller adds an additional {G}.

Forgotten Ancient

Whenever a player casts a spell, you may put a +1/+1 counter on this creature.
At the beginning of your upkeep, you may move any number of +1/+1 counters from this creature onto other creatures.

Hydra's Growth

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.

Lair of the Hydra

If you control two or more other lands, this land enters tapped.
{T}: Add {G}.
{X}{G}: Until end of turn, this land becomes an X/X green Hydra creature. It's still a land. X can't be 0.

Hydra

Branching Evolution

If one or more +1/+1 counters would be put on a creature you control, twice that many +1/+1 counters are put on that creature instead.

Colossification

Enchant creature
When this Aura enters, tap enchanted creature.
Enchanted creature gets +20/+20.

Hydra Broodmaster

{X}{X}{G}: Monstrosity X. (If this creature isn't monstrous, put X +1/+1 counters on it and it becomes monstrous.)
When this creature becomes monstrous, create X X/X green Hydra creature tokens.

Bow of Nylea

Attacking creatures you control have deathtouch.
{1}{G}, {T}: Choose one —
• Put a +1/+1 counter on target creature.
• Bow of Nylea deals 2 damage to target creature with flying.
• You gain 3 life.
• Put up to four target cards from your graveyard on the bottom of your library in any order.

Living Artifact

Enchant artifact
Whenever you're dealt damage, put that many vitality counters on this Aura.
At the beginning of your upkeep, you may remove a vitality counter from this Aura. If you do, you gain 1 life.

Primal Rage

Creatures you control have trample. (A creature with trample can deal excess combat damage to the player or planeswalker it's attacking.)

Pack Hunt

Search your library for up to three cards with the same name as target creature, reveal them, put them into your hand, then shuffle.

Wheel of Sun and Moon

Enchant player
If a card would be put into enchanted player's graveyard from anywhere, instead that card is revealed and put on the bottom of that player's library.

Nyxborn Hydra

Bestow {X}{G}{G} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached.)
Reach, trample
This permanent enters with X +1/+1 counters on it.
Enchanted creature gets +1/+1 for each +1/+1 counter on this Aura and has reach and trample.

Volrath's Laboratory

As this artifact enters, choose a color and a creature type.
{5}, {T}: Create a 2/2 creature token of the chosen color and type.

Hardened Scales

If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.

Hungering Hydra

This creature enters with X +1/+1 counters on it.
This creature can't be blocked by more than one creature.
Whenever this creature is dealt damage, put that many +1/+1 counters on it. (It must survive the damage to get the counters.)

Regenerate

Regenerate target creature. (The next time that creature would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

Doubling Season

If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead.
If an effect would put one or more counters on a permanent you control, it puts twice that many of those counters on that permanent instead.

Overgrowth

Enchant land
Whenever enchanted land is tapped for mana, its controller adds an additional {G}{G}.

Khalni Hydra

This spell costs {G} less to cast for each green creature you control.
Trample

Dragon Blood

{3}, {T}: Put a +1/+1 counter on target creature.

Hydra Trainer

You may exert this creature as it attacks. When you do, target creature gets +X/+X until end of turn, where X is the number of counters on permanents you control. (An exerted creature won't untap during your next untap step.)
{2}{G}: Adapt 2. (If this creature has no +1/+1 counters on it, put two +1/+1 counters on it.)

Giant Growth

Target creature gets +3/+3 until end of turn.

Treetop Bracers

Enchant creature (Target a creature as you cast this. This card enters attached to that creature.)
Enchanted creature gets +1/+1 and can't be blocked except by creatures with flying.

Managorger Hydra

Trample
Whenever a player casts a spell, put a +1/+1 counter on this creature.

Urban Burgeoning

Enchant land
Enchanted land has "Untap this land during each other player's untap step."