Fork

• WWizards of the Coast2004-10-04
  Official Ruling
  If you copy a spell for which Buyback has been paid, you get nothing back since the copied spell does not have a card to give you.
• WWizards of the Coast2004-10-04
  Official Ruling
  You need not (and may not) pay any additional mana or other costs (like sacrifices) to use the spell which is Forked. You get control over a complete copy but can change nothing except the targets.
• WWizards of the Coast2004-10-04
  Official Ruling
  It does copy the mana symbols in the mana cost for the card it is copying, but it uses its own color definition and not the one from those mana symbols. This is so it maintains its color just like the text says.
• WWizards of the Coast2004-10-04
  Official Ruling
  The copy that is placed on the stack is not considered to have been "cast".
• WWizards of the Coast2004-10-04
  Official Ruling
  For spells that can have a variable number of targets, the controller of the copy must use the same number of targets the original spell did.
• WWizards of the Coast2004-10-04
  Official Ruling
  Forking a spell with an X in the cost requires you to use the same X value.
• WWizards of the Coast2004-10-04
  Official Ruling
  When a spell with additional costs is copied, you don't have to pay those costs again.
• WWizards of the Coast2004-10-04
  Official Ruling
  If the spell being copied targets a spell on the stack, it is possible to target Fork itself since Fork is still on the stack when you pick the target(s) for the copy. Note that the copy's target will be illegal when it resolves.
• WWizards of the Coast2004-10-04
  Official Ruling
  If mana or other costs need to be spent at resolution of the spell, the player of Fork would still be responsible for paying that cost.
• WWizards of the Coast2004-10-04
  Official Ruling
  Fork will not copy changes made by modifying effects to the spell prior to the use of Fork, such as text-changing effects.
• WWizards of the Coast2004-10-04
  Official Ruling
  Fork does not let you make non-targeting choices about the spell.
• WWizards of the Coast2004-10-04
  Official Ruling
  The Fork card goes to the graveyard when it resolves and leaves the copy on the stack. There is no card representing the copy on the stack.
• WWizards of the Coast2004-12-01
  Official Ruling
  If you Fork a Spliced spell, the spliced text is added during the announcement of the original spell, and therefore is fully copied by Fork.
• WWizards of the Coast2009-05-01
  Official Ruling
  The copy will have the same mana cost as the original spell, but will be red rather than whatever color that mana cost would have made it.
• WWizards of the Coast2009-10-01
  Official Ruling
  If the targeted spell was kicked, then the copy will be kicked as well. If the targeted spell was not kicked, then the copy will not be kicked.

Rulings via Scryfall