Goomdiver

A Goomdiver is a diving-helmet clad Goomba that is found in Mario & Luigi: Superstar Saga. They appear in underwater locales, such as Oho Ocean.

Near-identical Goombas wearing diving helmets actually appeared earlier in Super Mario Land 2: 6 Golden Coins, known as Aqua Goombas. It is possible that Goomdivers were based on these enemies.