Amphibian Downpour

• 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.
• WOTC Official Reminder Textofficial rules
  Flash — You may cast this spell any time you could cast an instant.

• WWizards of the Coast2024-06-07
  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 Coast2024-06-07
  Official Ruling
  Amphibian Downpour may enchant a permanent that is only temporarily a creature, such as a Vehicle. If this happens, Amphibian Downpour's effect causes the enchanted permanent to remain a 1/1 blue Frog creature even after the temporary effect making it a creature expires.
• WWizards of the Coast2024-06-07
  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 Coast2024-06-07
  Official Ruling
  Amphibian Downpour overwrites all colors and creature types the enchanted creature has. It's just a blue Frog. The creature keeps any supertypes it has (such as legendary) but loses any other card types it has (such as artifact).
• WWizards of the Coast2024-06-07
  Official Ruling
  Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a creature may become lethal if Amphibian Downpour becomes attached to it during that turn.
• WWizards of the Coast2024-06-07
  Official Ruling
  You may choose new targets for any of the copies. You can make different choices for each copy.
• WWizards of the Coast2024-06-07
  Official Ruling
  If the enchanted creature gains an ability after Amphibian Downpour becomes attached to it, it will keep that ability.
• WWizards of the Coast2024-06-07
  Official Ruling
  Amphibian Downpour overwrites all previous effects that set the creature's base power and toughness to specific values. Any power- or toughness-setting effects that start to apply afterward will overwrite this effect.
• WWizards of the Coast2024-06-07
  Official Ruling
  If the enchanted creature has any subtypes other than creature types, such as Equipment, Vehicle, or Urza's, it loses those as well.
• WWizards of the Coast2024-06-07
  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 Coast2024-06-07
  Official Ruling
  Effects that modify the creature's power and/or toughness, such as the effect of Wing It, will apply to the creature no matter when they started to take effect. The same is true for counters that change its power and/or toughness and effects that switch its power and toughness.
• WWizards of the Coast2024-06-07
  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