Rampant Growth

Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Celestial Dawn

Lands you control are Plains.
Nonland permanents you control are white. The same is true for spells you control and nonland cards you own that aren't on the battlefield.
You may spend white mana as though it were mana of any color. You may spend other mana only as though it were colorless mana.

Jetmir, Nexus of Revels

Creatures you control get +1/+0 and have vigilance as long as you control three or more creatures.
Creatures you control also get +1/+0 and have trample as long as you control six or more creatures.
Creatures you control also get +1/+0 and have double strike as long as you control nine or more creatures.

Aysen Highway

White creatures have plainswalk. (They can't be blocked as long as defending player controls a Plains.)

Circuitous Route

Search your library for up to two basic land cards and/or Gate cards, put them onto the battlefield tapped, then shuffle.

Tundra Kavu

{T}: Target land becomes a Plains or an Island until end of turn.

Blood Moon

Magus of the Moon

Mountain

Plains

Nature's Lore

Search your library for a Forest card, put that card onto the battlefield, then shuffle.

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.

Righteous Avengers

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

Farseek

Search your library for a Plains, Island, Swamp, or Mountain card, put it onto the battlefield tapped, then shuffle.

Zodiac Rooster

Graceful Antelope

Plainswalk (This creature can't be blocked as long as defending player controls a Plains.)
Whenever this creature deals combat damage to a player, you may have target land become a Plains until this creature leaves the battlefield.

Conversion

At the beginning of your upkeep, sacrifice this enchantment unless you pay {W}{W}.
All Mountains are Plains.

Lush Growth

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

Forest

Mystic Compass

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

Unstable Frontier

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

Boggart Arsonists

Plainswalk (This creature can't be blocked as long as defending player controls a Plains.)
{2}{R}, Sacrifice this creature: Destroy target Scarecrow or Plains.