Rolling Thunder — ruling 1

You choose how many targets Rolling Thunder has and how the damage is divided as you cast the spell. Each target must receive at least 1 damage.

Rolling Thunder — ruling 2

If some, but not all, of the targets become illegal by the time Rolling Thunder tries to resolve, the original division of damage still applies, but no damage is dealt to illegal targets. If all the targets are illegal, the spell won’t resolve.

Rolling Thunder — ruling 3

If Rolling Thunder is copied, the copy will retain the original damage divsion. The spell or ability will likely allow you to choose new targets, but you can’t change the way damage is divided.

Rolling Thunder — ruling 4

If X is 0, you can’t choose any targets.

Rolling Thunder : règles, fonctionnement et interactions (MTG)

Rolling Thunder 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

Rolling Thunder deals X damage divided as you choose among any number of targets.

How it works : Rolling Thunder

Original English text — Wizards of the Coast / Scryfall

#1August 25, 2015· Wizards of the Coast
You choose how many targets Rolling Thunder has and how the damage is divided as you cast the spell. Each target must receive at least 1 damage.
No other card is named in this ruling.
#2August 25, 2015· Wizards of the Coast
If some, but not all, of the targets become illegal by the time Rolling Thunder tries to resolve, the original division of damage still applies, but no damage is dealt to illegal targets. If all the targets are illegal, the spell won’t resolve.
No other card is named in this ruling.
#3August 25, 2015· Wizards of the Coast
If Rolling Thunder is copied, the copy will retain the original damage divsion. The spell or ability will likely allow you to choose new targets, but you can’t change the way damage is divided.
No other card is named in this ruling.
#4October 4, 2004· Wizards of the Coast
If X is 0, you can’t choose any targets.
No other card is named in this ruling.