Deafening Silence will look at the entire turn to see if a player has cast a noncreature spell yet that turn, even if Deafening Silence wasn't on the battlefield when that spell was cast. Notably, you can't cast Deafening Silence and then cast another noncreature spell that turn.
04-10-2019
wotc
Players may cast any number of creature spells plus one noncreature spell each turn.
04-10-2019
wotc
If you cast a noncreature spell that was countered, you can't cast another noncreature spell that turn.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.