Daedream's Necklace

What is night?

This is a game state that changes via card effects. Being "night" does not inherently trigger any rules by itself, but certain cards have abilities that activate or become active while it is night. Additionally, if either player changes the state to night, the abilities of both players that become active while it is night become active for that duration.

Does an 【On Deploy】 ability activate even if the card is deployed from a zone other than the hand?

Yes, it activates. The 【On Deploy】 ability activates not only when deployed from the hand, but also when deployed from the deck, graveyard, or other zones by card effects.

With an ability that states "Choose up to X cards," can I choose 0 cards?

Yes, you can. Even if there are eligible cards to choose, by choosing 0 cards, you can effectively choose not to select any.

On my turn, I played an ability that states 〈It becomes night until the end of the opponent's next turn.〉 If the card that played this ability is put into the graveyard during the opponent's next turn, does it stop being night?

No, it does not stop being night. Even if the card that played this ability leaves the base, it is night until the end of the opponent's next turn.

I played a card that states 〈Choose up to 1 (specific) card from your hand and deploy it〉. What happens if there is no such specific card in my hand?

Choose 0 cards and resolve the rest of the effect.