Rakdos Firewheeler — ruling 1

If you can't target any opponent with Rakdos Firewheeler's ability, the ability doesn't go on the stack. You can't have it deal 2 damage to any creature or planeswalker. On the other hand, if you do choose two legal targets but either target is illegal when the ability tries to resolve, the other is still affected as appropriate.

Rakdos Firewheeler : règles, fonctionnement et interactions (MTG)

Rakdos Firewheeler 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, it deals 2 damage to target opponent and 2 damage to up to one target creature or planeswalker.

How it works : Rakdos Firewheeler

Original English text — Wizards of the Coast / Scryfall

#1January 25, 2019· Wizards of the Coast
If you can't target any opponent with Rakdos Firewheeler's ability, the ability doesn't go on the stack. You can't have it deal 2 damage to any creature or planeswalker. On the other hand, if you do choose two legal targets but either target is illegal when the ability tries to resolve, the other is still affected as appropriate.
No other card is named in this ruling.