Tendrils of Agony

• 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 Coast2022-12-08
  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 Coast2022-12-08
  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.
• WWizards of the Coast2022-12-08
  Official Ruling
  Spells cast from zones other than a player's hand and spells that were countered are counted by the storm ability.
• WWizards of the Coast2022-12-08
  Official Ruling
  You may choose new targets for any of the copies. You can make different choices for each copy.
• WWizards of the Coast2022-12-08
  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.

Rulings via Scryfall