Chandra, the Firebrand

If the spell Chandra copies has an X whose value was determined as it was cast (like Consume Spirit 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 costs that were paid for the original spell are copied as though those same costs were paid for the copy too. For example, if you sacrifice a 3/3 creature to cast Fling after activating Chandra's second ability, the copy of Fling will also deal 3 damage.

Chandra's second ability creates a delayed triggered ability that will copy the next instant or sorcery spell you cast that turn, regardless of whether that spell has targets.