Gauntlet of Power

As Gauntlet of Power enters the battlefield, choose a color.
Creatures of the chosen color get +1/+1.
Whenever a basic land is tapped for mana of the chosen color, its controller adds an additional one mana of that color.

Willow Dryad

Forestwalk (This creature can't be blocked as long as defending player controls a Forest.)

Forest

Vernal Bloom

Whenever a Forest is tapped for mana, its controller adds an additional {G}.

Mystic Compass

{1}, {T}: Target land becomes the basic land type of your choice until end of turn.

Mirri, Cat Warrior

First strike, forestwalk, vigilance (This creature deals combat damage before creatures without first strike, it can't be blocked as long as defending player controls a Forest, and attacking doesn't cause this creature to tap.)

Eldrazi Conscription

Enchant creature
Enchanted creature gets +10/+10 and has trample and annihilator 2. (Whenever it attacks, defending player sacrifices two permanents.)

Lumbering Satyr

All creatures have forestwalk. (They can't be blocked as long as defending player controls a Forest.)

Zodiac Rabbit

Mana Reflection

If you tap a permanent for mana, it produces twice as much of that mana instead.

Zodiac Tiger

Lush Growth

Enchant land
Enchanted land is a Mountain, Forest, and Plains.

Nyxbloom Ancient

Trample
If you tap a permanent for mana, it produces three times as much of that mana instead.

Unnatural Growth

At the beginning of each combat, double the power and toughness of each creature you control until end of turn.

Thelonite Monk

{T}, Sacrifice a green creature: Target land becomes a Forest. (This effect lasts indefinitely.)

Rancor

Enchant creature
Enchanted creature gets +2/+0 and has trample.
When Rancor is put into a graveyard from the battlefield, return Rancor to its owner's hand.

Zodiac Monkey

Vorinclex, Voice of Hunger

Trample
Whenever you tap a land for mana, add one mana of any type that land produced.
Whenever an opponent taps a land for mana, that land doesn't untap during its controller's next untap step.

Unstable Frontier

{T}: Add {C}.
{T}: Target land you control becomes the basic land type of your choice until end of turn.

Yavimaya, Cradle of Growth

Each land is a Forest in addition to its other land types.

Nissa, Who Shakes the World

Whenever you tap a Forest for mana, add an additional {G}.
+1: Put three +1/+1 counters on up to one target noncreature land you control. Untap it. It becomes a 0/0 Elemental creature with vigilance and haste that's still a land.
−8: You get an emblem with "Lands you control have indestructible." Search your library for any number of Forest cards, put them onto the battlefield tapped, then shuffle.