Gandalf, Westward Voyager

You can't choose to pay any additional costs for a copied spell. However, effects based on any additional costs that were paid for the original spell are copied as though those same costs were paid for the copy too.

The copy will have the same targets as the spell or ability it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. If the spell is a permanent spell with targets, such as an Aura, you may also choose a new target for that spell. The new targets must be legal. If, for any target, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).

The triggered ability and the copy it creates will resolve before the spell that caused the ability to trigger.

If a permanent spell is copied, it's put onto the battlefield as a token as the spell resolves rather than putting the copy of the spell onto the battlefield. The rules that apply to a permanent spell becoming a permanent apply to a copy of a spell becoming a token.

Any choices made when the spell resolves won't have been made yet when it's copied. Any such choices will be made separately when the copy resolves.

You create only one copy, no matter how many revealed cards share a card type with the spell you cast or how many card types those cards share with the spell you cast.

If the spell has damage divided as it was put onto the stack, the division can't be changed, although the targets receiving that damage still can. The same is true of spells that distribute counters to targets.

You copy the spell you cast, not any of the revealed cards.

Except in some very rare cases, the card each opponent draws will be the card revealed from the top of their library.

The token that a resolving copy of a spell becomes isn't said to have been "created" and won't interact with abilities that care about tokens being created, such as that of Rosie Cotton of South Lane.