It is a unique auto axe that deals much more damage than the original. It has a larger damage per hit and damage per second ratio compared to the standard auto axe (45 compared to 35) and uses less AP (50 compared to 65). Like all variants of the auto axe, it can never score a critical hit.
Auto axe, a modified and stronger version of the steel axe made out of old car parts.
Steel saw, a weaker version of the auto-axe that can be found on certain slaves.
Man Opener, a less strong unique variant that ignores armor(power armor included).
Though The Mauler is the single most damaging melee weapon (with the exception of the Shishkebab with the Pyromaniac perk), it is also the heaviest, making it a more difficult weapon to carry around.
As this weapon hits exceptionally fast for a melee weapon, using the perks Superior Defender and Ghoul Ecology can lead The Mauler to a much greater DPS stat.
Grinding barrels and other physics objects will usually result in damage, as they will be pulled violently into the player, then spat off in some random direction at a decent rate of speed proportional to the mass of the object; Cars will sometimes scoot towards you, barrels will hit a player hard enough to damage, and shopping carts rocket off like bats out of hell. It is possible to kill non-player characters with lots of patience and no repercussions, by repeatedly flinging barrels at them with The Mauler.
Behind the scenes
The fact that Everett mentions Monroeville, PA and chopping up ghouls with it is likely a reference to the fact that the Monroeville Mall was the location where the original Dawn of the Dead was filmed and in Night of the Living Dead the police and news casters call the zombies "ghouls". Also, "zombies" is a common derogatory name for ghouls.
Its animation doesn't loop correctly. If you continuously grind the air, you will notice the weapon "twitching" after several seconds, like the animation starting over again and again.
PlayStation 3PC When using it in FPS mode it may disappear mid-animation, bringing up the Pip-Boy immediately afterwards you will notice that your Pip-Boy has disappeared too (but not the screen). Changing to a different weapon quickly clears this bug.
Sometimes when you first equip and then use The Mauler, the Man Opener, or the auto axe, the spinning blades will disappear. Simply equip another weapon via Pip-Boy, and re equip the weapon and the blades should now remain visible.
↑The Lone Wanderer: "You got anything for me?" Everett: "All the metal you're bringing in, I suppose it's worth giving you something to really help with those Trogs. Here, this thing's mauled Trogs and Ghouls from here to Monroeville. Give it a whirl." (Everett's dialogue)