From the Super Mario Wiki
Magikoopa Mob is a Special Attack that Bowser uses in Mario & Luigi: Bowser's Inside Story and Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey. It requires fifteen SP to use in the original game, and seventeen BP (nineteen on Easy) to use in the remake. To use this move, Bowser must free the Magikoopas from Peach's Castle with the Red Key acquired from a Fawfulcopter on the second floor in the castle.
Once the move starts, the Magikoopas will line up in many designs: curves, L's, horizontal lines, vertical lines, etc, and the player has to use the to trace their position so Bowser can throw fireballs on the Magikoopas, which they then re-use to attack every opponent with their wands. When the wand has a yellow spark over it, Bowser throws a fireball on it. If all the Magikoopa's wands are touched, they create more damage than four or three of them alone. After about four or five times, the Magikoopas walk off the stage, exhausted.
In the remake, Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, Bowser shoots fireballs out of his mouth, rather than throwing them.
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