If dressed as the Silver Shroud, he'll refer to the Sole Survivor as such, and talks/acts similar to them and how they can "talk" like the Silver Shroud during certain dialogue options; most notably when talking to Hancock in-character.
Manta Man's Hit Points are based on the same scaling as the game's human companions, although unlike companions he cannot scale past level 50.
Because the Junk Jet cannot be properly used by NPCs, Manta Man is unable to equip it and is reduced to fighting with his fists if attacked by enemies while wandering the Wasteland. As a result, despite his above-average health he tends to fare extremely poorly in combat. Like all humanoid NPCs, it is possible for him to pick up and use weapons from a nearby corpse or container during combat, but this seldom occurs.
Unlike caravan merchants, provisioners, and settlers, Manta Man is not protected and can be killed by any wandering hostile enemies.
If he survives the fight, he can be encountered once more, this time fighting raiders or creatures.
A similar vigilante (and a villain) can be found in Fallout 3.