From the Super Mario Wiki
Robo-Drilldigger X is the more powerful form of Robo-Drilldigger who appears in the Battle Ring, as the first opponent faced in the Giant Luigi arena in Mario & Luigi: Dream Team. There are no major changes to his battle here. The main difference between Robo-Drilldigger and Robo-Drilldigger X is the version is red in color instead of gold. The player has to defeat it in 7 turns. To do so, the player must counter all attacks perfectly and make the maximum damage possible with Giant Luigi's Attacks.