Bonus Round

• WWizards of the Coast2018-06-08
  Official Ruling
  If the spell that’s copied is modal (that is, it says “Choose one —” or the like), the copy will have the same mode. Its controller can’t choose a different one.
• WWizards of the Coast2018-06-08
  Official Ruling
  The copy that Bonus Round’s ability creates is created on the stack, so it’s not “cast.” Abilities that trigger when a player casts a spell (like Bonus Round’s ability itself) won’t trigger.
• WWizards of the Coast2018-06-08
  Official Ruling
  The controller of the spell that caused Bonus Round’s ability to trigger also controls the copy.
• WWizards of the Coast2018-06-08
  Official Ruling
  The controller of the copy 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.
• WWizards of the Coast2018-06-08
  Official Ruling
  Bonus Round’s ability will copy any instant or sorcery spell, not just one with targets.
• WWizards of the Coast2018-06-08
  Official Ruling
  If the spell that’s copied has an X whose value was determined as it was cast, the copy has the same value of X.
• WWizards of the Coast2018-06-08
  Official Ruling
  A copy is created even if the spell that caused Bonus Round’s ability to trigger has been countered by the time that ability resolves. The copy resolves before the original spell.
• WWizards of the Coast2018-06-08
  Official Ruling
  The copy will have the same targets as the spell it’s copying unless its controller chooses new ones. That player may change any number of the targets, including all of them or none of them. The new targets must be legal.

Rulings via Scryfall