Twincast

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

The copy is created on the stack, so it's not "cast." Abilities that trigger when a player casts a spell won't trigger. The copy will resolve before the original spell does.

If the spell that's copied has an X whose value was determined as it was cast, the copy will have the same value of X.