Daybound and Nightbound

Daybound and Nightbound are a pair of keywords introduced in Innistrad: Midnight Hunt and also used in Innistrad: Crimson Vow.
==Description==
 
Daybound and Nightbound are static abilities.
When the game starts, it is neither day nor night. The most common way for this to change is for it to become day as a permanent with daybound appears on the battlefield. This occurs as the permanent enters the battlefield and does not use the stack. Spells and abilities can also explicitly cause it to become day or night. 
Once it's day or night, the game will be exactly one of those designations, day or night, until the game ends. A game cannot lose its day/night designation entirely, and the designation is the same for all players. 
If it's day, transforming double-faced cards with daybound and nightbound enter the battlefield with its daybound face up. If it's night, they enter nightbound face up. Note that cards with daybound/nightbound have the characteristics of their front (daybound) face while they are spells on the stack, even if it is currently night. 
There are two ways for the game's day/night designation to change. If it's day as a turn begins, and the previous turn's active player didn't cast a spell last turn, it becomes night. Similarly, if it's night as a turn begins, if the previous turn's active player cast two or more spells last turn, it becomes day. 
As it becomes day, all double-faced cards with nightbound transform to their daybound faces. As it becomes night, all double-faced cards with daybound transform to their nightbound faces. This does not use the stack, and is not a state-based action. Permanents with daybound and nightbound can't transform any other way.
To help players keep track of day and night, a helper card that reminds you of these rules is inserted into some booster packs of the relevant sets.
===Evaluation===
In retrospect, R&D considers daybound/nightbound to be a mistake, likely beause of the tracking issues and complicated game play. They don't expect to bring it back in a future Innistrad premier set.
==Rules==
===Rulings===
* Once the game has a day or night designation, whether that designation changes each turn is generally determined by the number of spells the active player cast on the previous turn. 
* Before a player untaps their permanents during the untap step, the game checks to see if the day/night designation should change.
* If it is day, and the active player of the previous turn cast no spells during their turn, it becomes night.
* If it is night, and the active player of the previous turn cast two or more spells during their turn, it becomes day.
* Double-faced permanents with daybound transform to their nightbound faces as it becomes night. Similarly, double-faced permanents with nightbound transform to their daybound faces as it becomes day. This happens immediately and is not a state-based action. It happens any time it becomes day or night, not just during the untap step.
* If you cast a spell with daybound during night, that spell will be front face up (that is, daybound face up) on the stack. However, it will enter the battlefield with its back face up (that is, with its nightbound face up). It won't enter with its daybound face up and then transform.
* If it is night, permanents with daybound that enter the battlefield without being cast will enter with their nightbound faces up.
* Permanents with daybound and nightbound can't transform via any means other than their daybound and nightbound abilities. Notably, older cards such as <c>Moonmist</c> that instruct a player to transform permanents don't affect permanents with daybound or nightbound.
* Once it has become day or become night, the game will have exactly one of those designations until the game is over. It can never be both day and night at the same time. Once it is day or night, the game can't return to being neither.
* The whole game is day or the whole game is night. It won't ever be day for one player and night for another.
* If it's neither day nor night, and a creature with daybound and a creature with nightbound somehow appear on the battlefield at the same time, it becomes day. The creature with nightbound will transform.
===Clarifications===
* If a nightbound permanent can't transform due to a card like <c>Immerwolf</c>, its nightbound face remains up even as it becomes day. If the effect preventing transformation ceases, it will immediately transform to "sync up" with the day/night cycle again. (The reverse applies to daybound permanents.)
==Examples==
==References==