Obsessive Astronomer

If it's neither day nor night, it becomes day as Obsessive Astronomer enters.
Whenever day becomes night or night becomes day, discard up to two cards, then draw that many cards.

Brimstone Vandal

Menace (This creature can't be blocked except by two or more creatures.)
If it's neither day nor night, it becomes day as Brimstone Vandal enters.
Whenever day becomes night or night becomes day, Brimstone Vandal deals 1 damage to each opponent.

Flame-Blessed Bolt

Flame-Blessed Bolt deals 2 damage to target creature or planeswalker. If that creature or planeswalker would die this turn, exile it instead.

Sunrise Cavalier

Trample, haste
If it's neither day nor night, it becomes day as Sunrise Cavalier enters.
Whenever day becomes night or night becomes day, put a +1/+1 counter on target creature you control.

Plains

Monk of the Open Hand

Flurry of Blows — Whenever you cast your second spell each turn, put a +1/+1 counter on Monk of the Open Hand.

Gavony Dawnguard

Ward {1}
If it's neither day nor night, it becomes day as Gavony Dawnguard enters.
Whenever day becomes night or night becomes day, look at the top four cards of your library. You may reveal a creature card with mana value 3 or less from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Clarion Spirit

Whenever you cast your second spell each turn, create a 1/1 white Spirit creature token with flying.

Mountain

Moonrager's Slash

This spell costs {2} less to cast if it's night.
Moonrager's Slash deals 3 damage to any target.

Fearsome Werewolf

Menace (This creature can't be blocked except by two or more creatures.)
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Fearful Villager

Menace (This creature can't be blocked except by two or more creatures.)
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Fearful Villager // Fearsome Werewolf

Usher of the Fallen

Boast — {1}{W}: Create a 1/1 white Human Warrior creature token. (Activate only if this creature attacked this turn and only once each turn.)

Harvesttide Assailant

Trample
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Harvesttide Infiltrator

Trample
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)