Rust Elemental — ruling 1

Sacrificing an artifact isn't optional. If you control an artifact other than Rust Elemental, you must sacrifice it. Otherwise, you must tap Rust Elemental and lose 4 life.

Rust Elemental : règles, fonctionnement et interactions (MTG)

Rust Elemental 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

Flying At the beginning of your upkeep, sacrifice another artifact. If you can't, tap this creature and you lose 4 life.

How it works : Rust Elemental

Original English text — Wizards of the Coast / Scryfall

#1December 1, 2004· Wizards of the Coast
Sacrificing an artifact isn't optional. If you control an artifact other than Rust Elemental, you must sacrifice it. Otherwise, you must tap Rust Elemental and lose 4 life.
No other card is named in this ruling.