Plasma mortar

The Plasma Mortar is the primary weapon of the Wraith and the Covenant Air Artillery.

Introduction
The Plasma mortar, fires huge ball of slowly moving superheated plasma with a large explosion radius and slow rate of fire. It is extremely powerful, usually kills infantry in a single hit and can destroy just about anything on the battlefield in a minimal amount of shots. Its plasma projectile moves relatively slowly, making it more susceptible to gravity, causing it to fire in an arc, like the Fuel Rod Gun, which allows for it to simply go over obstructions such as barricades and hills.

In the Halo novels, the physical effect of plasma weapons result in extreme heat and the melting/boiling of enemy armour. This effect is never shown in the Halo games, with the plasma having an explosive reaction instead.

Tactics

 * A Plasma Mortar fires in an arc so it is somewhat difficult to hit a target. The further away you are, the higher you will have to aim to actually hit the target.
 * Due to its slow-moving nature, the Plasma ball will be much easier to avoid than a human projectile.
 * Remember that even if you are behind cover, you may still not be protected from the plasma's curved trajectory.

Covenant Artillery
A giant stationary plasma mortar was seen destroying buildings in the Halo 2 E3 Demo video. Sergeant Banks called in an airstrike and a group of Longsword fighters flew in and destroyed it.

The stationary plasma mortar can be seen. on the beaches of New Mombasa in the Halo 2, but they are never seen firing. Several large plasma mortars can be seen destroying the Sentinel Factory ships on the level Quarantine Zone, but it's never confirmed if these are from stationary plasma mortar cannons, or otherwise.