Skulking Killer — ruling 1

Skulking Killer's ability triggers even if all your opponents control more than one creature. If the targeted creature's controller controls any other creatures as the ability resolves, the ability won't do anything. Notably, that player could cast a creature spell with flash or create a creature token in response to avoid the -2/-2 effect.

Skulking Killer : règles, fonctionnement et interactions (MTG)

Skulking Killer 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, target creature an opponent controls gets -2/-2 until end of turn if that opponent controls no other creatures.

How it works : Skulking Killer

Original English text — Wizards of the Coast / Scryfall

#1November 19, 2021· Wizards of the Coast
Skulking Killer's ability triggers even if all your opponents control more than one creature. If the targeted creature's controller controls any other creatures as the ability resolves, the ability won't do anything. Notably, that player could cast a creature spell with flash or create a creature token in response to avoid the -2/-2 effect.
No other card is named in this ruling.