Sentry Beam

Sentry Beams are metallic robots that make their only appearance in Super Mario Galaxy and its sequel Super Mario Galaxy 2 as enemies who try to defeat Mario by firing circular emanating lasers at him.

Super Mario Galaxy
Sentry Beams first appear in the Flipswitch Galaxy and then reappear later in the Battlerock Galaxy, Bowser Jr.'s Airship Armada, the Toy Time Galaxy and the Dreadnought Galaxy.

Super Mario Galaxy 2
In Super Mario Galaxy 2, they appear in a few galaxies, namely the Space Storm Galaxy, the Mario Squared Galaxy and the Grandmaster Galaxy.

Traits and Abilities
Sentry Beams are purple in appearance and somewhat resemble Topmen to some extent. They constantly remain stationary and attack by firing lasers in a circular ray-like shock wave formation. If they touch Mario, he will lose one section of his Health Meter. Sentry Beams will only fire these lasers when Mario gets near enough to them, and there is a limit as to how far they can go before they disappear. They cannot be destroyed by any means. However there is a way to stun the beams, temporarily stopping them from firing their lasers for several seconds and giving Mario refuge from their barrage of attacks. If Mario either jumps on top of the robot or fires a Star Bit at it then the robot will become stunned and the spring beneath its head becomes exposed and Mario can then use them like a trampoline. Some of these purple robots do not fire lasers, but still have a springy neck nevertheless.

There are also very rare types of Sentry Beam, one has a nut on top of it, while one has a bolt. They're both found in Buoy Base Galaxy in Super Mario Galaxy on the Poké Ball Planet, with the nut-like robot on the bottom of the planet and the bolt-like robot on the top. The Sentry Beam with the nut is like the original purple robot with no springy neck, but once Mario or Luigi spins on the bolt of the bolt Sentry Beam, the planet opens up to reveal the Power Star.

Sentry Beams also have a spiked yellow variant which attacks in the same way as its purple counterpart, but due to its spikes Mario cannot stun it, they also lack eyes.

The final variant of Sentry Beam is a gray, undefeatable, mobile unit with sinister-looking eyes, which hovers around with the aid of a propeller at its bottom. This variant can shoot a straight laser beam at Mario from its mouth that is very fast and very hard to dodge. If Mario stands on its head it will cease all action but once Mario starts moving again it will continue with its attack.

All Sentry Beams are invincible, they cannot be defeated by anything less than Rainbow Mario himself. Mario can throw Bob-ombs at the robots but they will still not be destroyed and will resume their attack momentarily.