Corrosion | Magic: The Gathering
Formats Corrosion is Legal in
Official Oracle Text for Corrosion
At the beginning of your upkeep, put a rust counter on each artifact target opponent controls. Then destroy each artifact with converted mana cost less than or equal to the number of rust counters on it. Artifacts destroyed this way can't be regenerated.
When Corrosion leaves the battlefield, remove all rust counters from all permanents.
Official Rulings for Corrosion
10/4/2004 : In multiplayer games, you can choose a new target player each upkeep.
2/1/2006 : Only puts rust counters on artifacts your opponents control, but destroys all artifacts with rust counters on them, even your own. When it leaves the battlefield, it removes all rust counters, not just those that happen to be on artifacts.