Plains

Honest Rutstein

When Honest Rutstein enters, return target creature card from your graveyard to your hand.
Creature spells you cast cost {1} less to cast.

Outlaw Medic

Lifelink
When Outlaw Medic dies, draw a card.

Forest

Ancient Cornucopia

Whenever you cast a spell that's one or more colors, you may gain 1 life for each of that spell's colors. Do this only once each turn.
{T}: Add one mana of any color.

Throw from the Saddle

Target creature you control gets +1/+1 until end of turn. Put a +1/+1 counter on it instead if it's a Mount. Then it deals damage equal to its power to target creature you don't control.

Drover Grizzly

Whenever Drover Grizzly attacks while saddled, creatures you control gain trample until end of turn.
Saddle 1 (Tap any number of other creatures you control with total power 1 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)

Forlorn Flats

Forlorn Flats enters tapped.
When Forlorn Flats enters, it deals 1 damage to target opponent.
{T}: Add {W} or {B}.

Voracious Varmint

Vigilance
{1}, Sacrifice Voracious Varmint: Destroy target artifact or enchantment.

Prairie Dog

Lifelink
At the beginning of your end step, if you haven't cast a spell from your hand this turn, put a +1/+1 counter on Prairie Dog.
{4}{W}: Until end of turn, if you would put one or more +1/+1 counters on a creature you control, put that many plus one +1/+1 counters on it instead.

Holy Cow

Flash
Flying
When Holy Cow enters, you gain 2 life and scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Miriam, Herd Whisperer

During your turn, Mounts and Vehicles you control have hexproof.
Whenever a Mount or Vehicle you control attacks, put a +1/+1 counter on it.

Bridled Bighorn

Vigilance
Whenever Bridled Bighorn attacks while saddled, create a 1/1 white Sheep creature token.
Saddle 2 (Tap any number of other creatures you control with total power 2 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)

Swamp

Thunder Lasso

When Thunder Lasso enters, attach it to target creature you control.
Equipped creature gets +1/+1.
Whenever equipped creature attacks, tap target creature defending player controls.
Equip {2}

Creosote Heath

Creosote Heath enters tapped.
When Creosote Heath enters, it deals 1 damage to target opponent.
{T}: Add {G} or {W}.

Sterling Keykeeper

Fierce Retribution

Cleave {5}{W} (You may cast this spell for its cleave cost. If you do, remove the words in square brackets.)
Destroy target [attacking] creature.

Freestrider Lookout

Reach
Whenever you commit a crime, look at the top five cards of your library. You may put a land card from among them onto the battlefield tapped. Put the rest on the bottom of your library in a random order. This ability triggers only once each turn. (Targeting opponents, anything they control, and/or cards in their graveyards is a crime.)

Stubborn Burrowfiend

Whenever Stubborn Burrowfiend becomes saddled for the first time each turn, mill two cards, then Stubborn Burrowfiend gets +X/+X until end of turn, where X is the number of creature cards in your graveyard.
Saddle 2 (Tap any number of other creatures you control with total power 2 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)

Frontier Seeker

When Frontier Seeker enters, look at the top five cards of your library. You may reveal a Mount creature card or a Plains card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Abrupt Decay

This spell can't be countered.
Destroy target nonland permanent with mana value 3 or less.

Dust Animus

Flying
If you control five or more untapped lands, Dust Animus enters with two +1/+1 counters and a lifelink counter on it.
Plot {1}{W} (You may pay {1}{W} and exile this card from your hand. Cast it as a sorcery on a later turn without paying its mana cost. Plot only as a sorcery.)

Desert's Due

Target creature gets -2/-2 until end of turn. It gets an additional -1/-1 until end of turn for each Desert you control.

Bounding Felidar

Whenever Bounding Felidar attacks while saddled, put a +1/+1 counter on each other creature you control. You gain 1 life for each of those creatures.
Saddle 2 (Tap any number of other creatures you control with total power 2 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)

Congregation Gryff

Flying, lifelink
Whenever Congregation Gryff attacks while saddled, it gets +X/+X until end of turn, where X is the number of Mounts you control.
Saddle 3 (Tap any number of other creatures you control with total power 3 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)