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Mario & Luigi: Superstar Saga / Mario & Luigi: Superstar Saga + Bowser's Minions
In Mario & Luigi: Superstar Saga, some enemies have the ability to change the Mario Bros' stats. If their speed goes down, enemies may get to attack before Mario or Luigi. The ailment is indicated by a streaking blue flash with an arrow pointing down.
Mario & Luigi: Partners in Time
SPD-Down is the same status ailment in Mario & Luigi: Partners in Time. It is indicated by a shrinking blue circle around the afflicted. Ice Flowers can randomly inflict this status ailment on enemies.
Mario & Luigi: Bowser's Inside Story / Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey
Again, SPD-Down makes an appearance in Mario & Luigi: Bowser's Inside Story. Blue streaks flowing downward indicate the affected. Only Durmite and Durmite X can cause this to the bros. Just like in Mario & Luigi: Superstar Saga + Bowser's Minions, a First Strike with a hammer in Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey will cause enemies to start the battle with this status effect.
Mario & Luigi: Paper Jam