Yarok's Wavecrasher — ruling 1

If you control no other creatures when the triggered ability resolves, you simply don't return anything. There's no penalty for being unable to do so.

Yarok's Wavecrasher : règles, fonctionnement et interactions (MTG)

Yarok's Wavecrasher 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, return another creature you control to its owner's hand.

How it works : Yarok's Wavecrasher

Original English text — Wizards of the Coast / Scryfall

#1July 12, 2019· Wizards of the Coast
If you control no other creatures when the triggered ability resolves, you simply don't return anything. There's no penalty for being unable to do so.
No other card is named in this ruling.