Weed-Pruner Poplar — ruling 1

The ability is mandatory. If you’re the only player who controls any other creatures, you must target one of your own creatures with the ability.

Weed-Pruner Poplar : règles, fonctionnement et interactions (MTG)

Weed-Pruner Poplar 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

At the beginning of your upkeep, target creature other than this creature gets -1/-1 until end of turn.

How it works : Weed-Pruner Poplar

Original English text — Wizards of the Coast / Scryfall

#1April 1, 2008· Wizards of the Coast
The ability is mandatory. If you’re the only player who controls any other creatures, you must target one of your own creatures with the ability.
No other card is named in this ruling.