Chatterstorm

• WOTC Official Reminder Textofficial rules
  Storm — When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.

• WWizards of the Coast2021-06-18
  Official Ruling
  A copy of a spell can be countered like any other spell, but it must be countered individually. Countering a spell with storm won't affect the copies.
• WWizards of the Coast2021-06-18
  Official Ruling
  If a spell with storm has targets, you may choose new targets for any of the copies. You can make different choices for each copy.
• WWizards of the Coast2021-06-18
  Official Ruling
  The copies are put directly onto the stack. They aren't cast and won't be counted by other spells with storm cast later in the turn.
• WWizards of the Coast2021-06-18
  Official Ruling
  Spells cast from zones other than a player's hand and spells that were countered or otherwise failed to resolve are counted by the storm ability.
• WWizards of the Coast2021-06-18
  Official Ruling
  The triggered ability that creates the copies can itself be countered by anything that can counter a triggered ability. If it is countered, no copies will be put onto the stack.

Rulings via Scryfall

• WO
  Wizards of the Coast2021-09-08

  Chatterstorm was banned in pauper on September 8, 2021. Storm combo decks had the highest non-mirror match win rate among top decks and earned by far the most 5–0 performances in Magic Online leagues. These decks use fast mana to power out a large Chatterstorm, often in combination with First Day of Class, to create an insurmountable board state or even win the game on the spot. Therefore, to address Storm's high win rate, high metagame share, and difficulty to interact with, we are banning Chatterstorm. Source: https://magic.wizards.com/en/news/news/september-8-2021-banned-and-restricted-announcement