Lignify

Enchant creature
Enchanted creature is a Treefolk with base power and toughness 0/4 and loses all abilities.

Staff of Titania

Equipped creature gets +X/+X, where X is the number of Forests you control.
Whenever equipped creature attacks, create a 1/1 green Forest Dryad land creature token. (It's affected by summoning sickness.)
Equip {3}

Cultivate

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Gaea's Touch

{0}: You may put a basic Forest card from your hand onto the battlefield. Activate only as a sorcery and only once each turn.
Sacrifice Gaea's Touch: Add {G}{G}.

Gaea's Bounty

Search your library for up to two Forest cards, reveal those cards, put them into your hand, then shuffle.

Vinelasher Kudzu

Landfall — Whenever a land you control enters, put a +1/+1 counter on Vinelasher Kudzu.

Song of the Dryads

Enchant permanent
Enchanted permanent is a colorless Forest land.

Forest

Thelonite Druid

{1}{G}, {T}, Sacrifice a creature: Forests you control become 2/3 creatures until end of turn. They're still lands.

Primeval Titan

Trample
Whenever Primeval Titan enters or attacks, you may search your library for up to two land cards, put them onto the battlefield tapped, then shuffle.

Druid Class

(Gain the next level as a sorcery to add its ability.)
Landfall — Whenever a land you control enters, you gain 1 life.
{2}{G}: Level 2
You may play an additional land on each of your turns.
{4}{G}: Level 3
When this Class becomes level 3, target land you control becomes a creature with haste and "This creature's power and toughness are each equal to the number of lands you control." It's still a land.

Dryad Arbor

(Dryad Arbor isn't a spell, it's affected by summoning sickness, and it has "{T}: Add {G}.")

Kudzu

Enchant land
When enchanted land becomes tapped, destroy it. That land's controller may attach Kudzu to a land of their choice.

Naturalize

Prevent all combat damage that would be dealt this turn.

Gaea's Liege

As long as Gaea's Liege isn't attacking, its power and toughness are each equal to the number of Forests you control. As long as Gaea's Liege is attacking, its power and toughness are each equal to the number of Forests defending player controls.
{T}: Target land becomes a Forest until Gaea's Liege leaves the battlefield.

Primal Rage

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

Dungrove Elder

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
Dungrove Elder's power and toughness are each equal to the number of Forests you control.