Kuldotha Flamefiend — ruling 1

You divide the damage as Kuldotha Flamefiend's triggered ability is put onto the stack, not as it resolves. Each target must be assigned at least 1 damage. You can't choose more than 4 targets and assign 0 damage to a target.

Kuldotha Flamefiend — ruling 2

You may choose zero targets. If you do, Kuldotha Flamefiend deals no damage, but you may sacrifice an artifact.

Kuldotha Flamefiend — ruling 3

If some of the targets become illegal for Kuldotha Flamefiend's ability, the original division of damage still applies, but the damage that would have been dealt to illegal targets isn't dealt at all. If all of the targets become illegal, you can't sacrifice an artifact.

Kuldotha Flamefiend — ruling 4

You don't choose whether to sacrifice an artifact or which artifact you're sacrificing until the ability resolves. Once you decide to sacrifice an artifact (or not), it's too late for players to respond.

Kuldotha Flamefiend : règles, fonctionnement et interactions (MTG)

Kuldotha Flamefiend 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

When this creature enters, you may sacrifice an artifact. If you do, this creature deals 4 damage divided as you choose among any number of targets.

How it works : Kuldotha Flamefiend

Original English text — Wizards of the Coast / Scryfall

#1August 7, 2020· Wizards of the Coast
You divide the damage as Kuldotha Flamefiend's triggered ability is put onto the stack, not as it resolves. Each target must be assigned at least 1 damage. You can't choose more than 4 targets and assign 0 damage to a target.
No other card is named in this ruling.
#2August 7, 2020· Wizards of the Coast
You may choose zero targets. If you do, Kuldotha Flamefiend deals no damage, but you may sacrifice an artifact.
No other card is named in this ruling.
#3August 7, 2020· Wizards of the Coast
If some of the targets become illegal for Kuldotha Flamefiend's ability, the original division of damage still applies, but the damage that would have been dealt to illegal targets isn't dealt at all. If all of the targets become illegal, you can't sacrifice an artifact.
No other card is named in this ruling.
#4August 7, 2020· Wizards of the Coast
You don't choose whether to sacrifice an artifact or which artifact you're sacrificing until the ability resolves. Once you decide to sacrifice an artifact (or not), it's too late for players to respond.
No other card is named in this ruling.