Dualcaster Mage

If the spell has an X whose value was determined as it was cast (like Earthquake does), the copy has the same value of X.

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

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, for one of the targets, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).