The Celestus

If it's neither day nor night, it becomes day as The Celestus enters.
{T}: Add one mana of any color.
{3}, {T}: If it's night, it becomes day. Otherwise, it becomes night. Activate only as a sorcery.
Whenever day becomes night or night becomes day, you gain 1 life. You may draw a card. If you do, discard a card.

Firmament Sage

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

Component Collector

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

Into the Night

It becomes night. Discard any number of cards, then draw that many cards plus one.

Sunstreak Phoenix

Flying
If it's neither day nor night, it becomes day as Sunstreak Phoenix enters.
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.

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.

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.

Vadrik, Astral Archmage

If it's neither day nor night, it becomes day as Vadrik, Astral Archmage enters.
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.