From the Super Mario Wiki
Dark Trashures are dark 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. They also have the highest health out of all non-boss enemies.
Names in Other Languages
||From "oscuro" (dark) "cofre" (chest) and "fraude" (fraud)
||From coffre (chest), the familiar word "fortiche" (easy) and "noir" (black).