Ironically, the weapon is very powerful against Brutes.
The gravity hammer is an excellent anti-Flood weapon. It is capable of killing multiple Flood forms in one swing due to its massive shock wave.
Try to use it against large groups of fleeing Grunts. The shockwave will kill any surrounding Grunts that are close to the one you hit. Also, if the Brute chieftain in the area has been killed, taking out the gravity hammer will cause the Grunts to panic.
Reserve usage of the gravity hammer for priority targets, such as high-ranking Brutes or tank forms. It will normally kill them in one hit.
This weapon's usefulness increases when you use the Cowbell Skull, as things will fly farther when you hit them. This would also increase the risk of being killed while dealing with gravity hammer-wielding Brutes, however.
In Halo 4, the gravity hammer is obtainable only in the final mission (where it appears in an armory mostly full of Forerunner weapons), but can be obtained earlier in Shutdown via a Legendaryco-op-exclusive secret. For more information, see this page.
The gravity hammer is best used as a secondary weapon to pull out if faced with nearby foes on a ledge, an incoming vehicle, or a grenade coming towards the player. The hammer is apt at dealing with all three of these threats.
The gravity hammer's blast can go through walls and floors, and this can be used to hit players in an adjacent room.
The gravity hammer can be used to propel the player higher than normal, if the player times the attack as they jump, it will elevate them farther and higher. You can gain just as much height as a grenade jump with very little or no risk.
Try hammering enemy Warthogs and Mongooses on Rat's Nest near the rocket launcher spawn point. It can result in the vehicle sailing to the death barrier.
If you time the shock wave from the hammer at the right time you can send rockets and missiles in another direction.
The hammer may be known as a great CQB weapon, but it is slower to compete against the shotgun. Also, even though the energy sword lunges slightly slower, it has a farther lunge and can parry your attacks, but you cannot parry the sword carrier's attacks. If you find yourself up against one of these weapons, create space between you and your opponent (you can knock him back with the shockwave if he's too close) and change to a long-range weapon to take down the enemy. It is important to remember that Mauler wielders are considered easy targets for the gravity hammer.
Try combining a gravity hammer jump and grenade jump to get to spots that aren't normally reachable for an advantage.
It is possible to stick a plasma or spike grenade on the end of the hammer.
In Halo 5: Guardians, the hammer can now be used with Smart-Link to increase the lunge range of the weapon. In addition, it has three additional variants:
Corpsemaker, an improved hammer with faster swinging and weapon draw/switch speeds, making it more effective in melee weapon clashes (including other hammers).
Grinder, an advanced hammer with an electromagnetic vortex effect that can temporarily disable vehicles and suck in any foe who gets too close, resulting in extreme damage.
Tartarus' Gavel, a mythic hammer with boosts to movement speed, shield strength, jump height, and Ground Pound damage along with the ability to create linear explosions that track nearby enemies and deal massive damage to groups of nearby enemies, making it a competitor to the Prophets' Bane.