Mercurial Spelldancer

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 is created on the stack, so it's not "cast." Creating the copy won't cause abilities that trigger when a player casts a spell to trigger.

The copy will have the same targets as the spell 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).