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Mario & Luigi series
Mario & Luigi: Superstar Saga
Some enemies have the ability to change the Mario Bros' stats. If their defense power goes down, enemy attacks will do more damage. The ailment is indicated by a gray block with an arrow pointing down.
Mario & Luigi: Partners in Time
DEF-Down is the same status ailment in this game. Its indicator is a shrinking green circle around the afflicted. Ice Flowers can randomly inflict this status ailment on enemies.
Mario & Luigi: Bowser's Inside Story
Again, DEF-Down makes an appearance. Green streaks flowing downward indicate the affected. Many enemies can inflict this status on one of the bros, mainly enemies with the power to electrocute the bros such as Alpha Kretin. One of Mario & Luigi's special moves, Falling Star, can inflict this status on enemies.
Mario & Luigi: Dream Team
DEF-Down once again makes an appearance, visually the same as Mario & Luigi: Bowser's Inside Story. Green streaks flowing downward and black flashing indicate the affected. Many enemies can inflict this status on one of the bros. This status can be inflicted on enemies using a Virus-Master badge combo, or a Risk-Bronze badge combo (though the latter is less likely to do so, and it can affect the bros.)
Paper Mario series
Paper Mario: The Thousand-Year Door
The status ailment returns in this game and serves much the same purpose (specifically, lowering defences by 3 points), however if it known as the "Soft" status. It is indicated by a gray diamond with an arrow pointing down. Using a Mr. Softener can give this status effect to enemies, however, the enemies can also do the same to Mario.