From the Super Mario Wiki
They inhabit the Oho Ocean Seabed and the underwater portions of Gwarhar Lagoon and only appear in battle, never on the field. Their only method of attack is firing several Bullet Bills at Mario and Luigi. A Mecha-Blooper has a total of five torpedoes to shoot, and can fire off any number of them during its attack. However, once all five have been fired, the Mecha-Blooper must spend a turn to reload. They are especially vulnerable to Luigi's Thunderhand, and if a Mecha-Blooper is attacked but not defeated, a "!" will appear above it and will automatically counterattack.
The Bullet Bills they shoot are the only example of a Bullet Bill in Mario & Luigi: Superstar Saga + Bowser's Minions to not be updated to resemble the current Bullet Bill design. Due to only appearing underwater, they are also fully absent from the new Minion Quest: The Search for Bowser mode.
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