From the Super Mario Wiki
Dark Trashures are dark purple forms of the Trashure. Found in Peach's Castle during the events of Mario & Luigi: Bowser's Inside Story, these enemies are stronger than their original forms, throwing faster and more harmful items and less Mushrooms and coins. Although they have more power, they are also more prone to running away and leaving the player with no EXP. Like normal Trashures, if the player does not counter the hammer from the Dark Trashure, Bowser may get stunned making them wait a few turns. They also have the highest health out of all non-boss enemies excluding ones encountered in The Gauntlet. They are mostly seen in battle with Dark Mechawfuls or Naplocks and appear to be working for the evil Fawful though this is unknown if they do. Bowser can use the Vacuum Block to inhale a Blitty from Dark Trashures.
In the original game, Mario and Luigi cannot fight Dark Trashures but only their normal counterpart; however, with cheats enabled and fighting them, the battle acts normally. Its attacks can be dodged except when they throw a cannonball at a rapid speed.
In Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, they no longer throw Scutlets at Bowser during their attacks.
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