Celestus Sanctifier

If it's neither day nor night, it becomes day as Celestus Sanctifier enters the battlefield.
Whenever day becomes night or night becomes day, look at the top two cards of your library. Put one of them into your graveyard.

Gavony Dawnguard

Ward {1}
If it's neither day nor night, it becomes day as Gavony Dawnguard enters the battlefield.
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.

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 the battlefield.
Whenever day becomes night or night becomes day, Brimstone Vandal deals 1 damage to each opponent.

Vadrik, Astral Archmage

If it's neither day nor night, it becomes day as Vadrik, Astral Archmage enters the battlefield.
Instant and sorcery spells you cast cost {X} less to cast, where X is Vadrik's power.
Whenever day becomes night or night becomes day, put a +1/+1 counter on Vadrik.

Obsessive Astronomer

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

Sunstreak Phoenix

Flying
If it's neither day nor night, it becomes day as Sunstreak Phoenix enters the battlefield.
Whenever day becomes night or night becomes day, you may pay {1}{R}. If you do, return Sunstreak Phoenix from your graveyard to the battlefield tapped.

Vadrok, Apex of Thunder

Mutate {1}{W/U}{R}{R} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Flying, first strike
Whenever this creature mutates, you may cast target noncreature card with mana value 3 or less from your graveyard without paying its mana cost.

Sunrise Cavalier

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

Component Collector

If it's neither day nor night, it becomes day as Component Collector enters the battlefield.
Whenever day becomes night or night becomes day, you may tap or untap target nonland permanent.

Spellrune Howler

Whenever you cast an instant or sorcery spell, Spellrune Howler gets +2/+2 until end of turn.
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Spellrune Painter

Whenever you cast an instant or sorcery spell, Spellrune Painter gets +1/+1 until end of turn.
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Spellrune Painter // Spellrune Howler

Moonrage Brute

First strike
Ward—Pay 3 life.
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Brutal Cathar

When this creature enters the battlefield or transforms into Brutal Cathar, exile target creature an opponent controls until this creature leaves the battlefield.
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Brutal Cathar // Moonrage Brute

Dennick, Pious Apparition

Flying
Whenever one or more creature cards are put into graveyards from anywhere, investigate. This ability triggers only once each turn. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")
If Dennick, Pious Apparition would be put into a graveyard from anywhere, exile it instead.

Dennick, Pious Apprentice

Lifelink
Cards in graveyards can't be the targets of spells or abilities.
Disturb {2}{W}{U} (You may cast this card from your graveyard transformed for its disturb cost.)

Dennick, Pious Apprentice // Dennick, Pious Apparition

Moonveil Regent

Flying
Whenever you cast a spell, you may discard your hand. If you do, draw a card for each of that spell's colors.
When Moonveil Regent dies, it deals X damage to any target, where X is the number of colors among permanents you control.

Firmament Sage

If it's neither day nor night, it becomes day as Firmament Sage enters the battlefield.
Whenever day becomes night or night becomes day, draw a card.

Sevinne, the Chronoclasm

Prevent all damage that would be dealt to Sevinne, the Chronoclasm.
Whenever you cast your first instant or sorcery spell from your graveyard each turn, copy that spell. You may choose new targets for the copy.