Dual Casting — ruling 1

The ability granted by Dual Casting can target (and copy) any instant or sorcery spell you control, not just one with targets.

Dual Casting — ruling 2

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 then resolve like a normal spell, after players get a chance to cast spells and activate abilities.

Dual Casting — ruling 3

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).

Dual Casting — ruling 4

If the spell being copied is modal (that is, it says “Choose one —” or the like), the copy will have the same mode(s). You can’t choose different ones.

Dual Casting — ruling 5

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

Dual Casting — ruling 6

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 and then copy it with the ability granted by Dual Casting, the copy of Fling will also deal 3 damage to its target.

Dual Casting : règles, fonctionnement et interactions (MTG)

Dual Casting is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Enchant creature Enchanted creature has ", : Copy target instant or sorcery spell you control. You may choose new targets for the copy."

How it works : Dual Casting

Original English text — Wizards of the Coast / Scryfall

#1May 1, 2012· Wizards of the Coast
The ability granted by Dual Casting can target (and copy) any instant or sorcery spell you control, not just one with targets.
No other card is named in this ruling.
#2May 1, 2012· Wizards of the Coast
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 then resolve like a normal spell, after players get a chance to cast spells and activate abilities.
No other card is named in this ruling.
#3May 1, 2012· Wizards of the Coast
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).
No other card is named in this ruling.
#4May 1, 2012· Wizards of the Coast
If the spell being copied is modal (that is, it says “Choose one —” or the like), the copy will have the same mode(s). You can’t choose different ones.
No other card is named in this ruling.
#5May 1, 2012· Wizards of the Coast
If the spell being copied has an X whose value was determined as it was cast (like Earthquake does), the copy has the same value of X.
No other card is named in this ruling.
#6May 1, 2012· Wizards of the Coast
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 and then copy it with the ability granted by Dual Casting, the copy of Fling will also deal 3 damage to its target.
No other card is named in this ruling.