Dragonlord Atarka — ruling 1

You choose how many targets the ability has and how the damage is divided as you put the ability on the stack. Each target must receive at least 1 damage.

Dragonlord Atarka — ruling 2

If some of the targets are illegal targets as the ability tries to resolve, the original division of damage still applies but no damage is dealt to the illegal targets. If all targets are illegal, the ability doesn’t resolve.

Dragonlord Atarka : règles, fonctionnement et interactions (MTG)

Dragonlord Atarka 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

Flying, trample When Dragonlord Atarka enters, it deals 5 damage divided as you choose among any number of target creatures and/or planeswalkers your opponents control.

How it works : Dragonlord Atarka

Original English text — Wizards of the Coast / Scryfall

#1February 25, 2015· Wizards of the Coast
You choose how many targets the ability has and how the damage is divided as you put the ability on the stack. Each target must receive at least 1 damage.
No other card is named in this ruling.
#2February 25, 2015· Wizards of the Coast
If some of the targets are illegal targets as the ability tries to resolve, the original division of damage still applies but no damage is dealt to the illegal targets. If all targets are illegal, the ability doesn’t resolve.
No other card is named in this ruling.