Gigantiform

• WOTC Official Reminder Textofficial rules
  Kicker — Kicker [cost] (You may pay an additional [cost] as you cast this spell.)

• WWizards of the Coast2009-10-01
  Official Ruling
  Effects that modify the enchanted creature's power or toughness, such as the effects of Giant Growth or Glorious Anthem, will apply to it no matter when they started to take effect. The same is true for counters that change the creature's power or toughness (such as +1/+1 counters) and effects that switch its power and toughness.
• WWizards of the Coast2009-10-01
  Official Ruling
  Although the Gigantiform cast as a spell targets a creature, the Gigantiform put onto the battlefield as a result of the first one's triggered ability does not. It may be attached to a creature with shroud, for example. However, it may not be attached to a creature that couldn't be enchanted by it, such as a creature with protection from green. You don't choose which creature it will be attached to until it enters. Once you choose which creature to attach it to, it's too late for players to respond.
• WWizards of the Coast2009-10-01
  Official Ruling
  Gigantiform overwrites all previous effects that set the enchanted creature's power and toughness to specific values. Other effects that set its power or toughness to specific values that start to apply after Gigantiform becomes attached to it will overwrite Gigantiform.
• WWizards of the Coast2009-10-01
  Official Ruling
  If the creature targeted by the Gigantiform spell is an illegal target by the time Gigantiform resolves, the spell doesn't resolve. It won't enter, so you won't get to search your library for another Gigantiform.
• WWizards of the Coast2024-11-08
  Official Ruling
  If a card or token enters as a copy of a permanent, the new permanent isn't kicked, even if the original was.
• WWizards of the Coast2024-11-08
  Official Ruling
  If you put a permanent with a kicker ability onto the battlefield without casting it, you can't kick it.
• WWizards of the Coast2024-11-08
  Official Ruling
  If you copy a kicked spell on the stack, the copy is also kicked. If the copied spell is a permanent spell, the token the copy of that spell becomes when it enters is also kicked.
• WWizards of the Coast2024-11-08
  Official Ruling
  If a spell's kicker cost was paid, the spell is "kicked."
• WWizards of the Coast2024-11-08
  Official Ruling
  The kicker ability doesn't let you pay a kicker cost more than once.
• WWizards of the Coast2024-11-08
  Official Ruling
  To determine a spell's total cost, start with the mana cost (or an alternative cost if another card's effect allows you to pay one instead), add any cost increases (such as kicker), then apply any cost reductions. The spell's mana value remains unchanged, no matter what the total cost to cast it was.

Rulings via Scryfall