The Plasma Cannon is a devastating ranged weapon that shoots explosive projectiles on a slightly undulating trajectory.
Firing recklessly is very hazardous, however, and the weapon is as much a threat to yourself as it is to your enemies. Fire each shot with careful consideration to avoid yet another stupid death -- even if the shot or recoil doesn't kill you, rocks and arrows sent flying by the explosion certainly can!
The recoil is more substantial than other ranged weapons, throwing back the Spelunker four full tiles when fired, and standing too close to the target area will cause you to be caught in the explosion. You should also be careful not to destroy essential platforms and cut off access to the area above yourself if you don't have ropes or any other means of reaching high ledges.
The Plasma Cannon's recoil is also strong enough to throw you off of a rope, so using a rope will not help you stabilize yourself when using the Plasma Cannon.
The Plasma Cannon does not run out of energy and has unlimited ammunition.
The plasma cannon is probably a nod to the Halo series, and bears strong similarities to several of the Covenant plasma weapons, such as the Plasma Repeater in appearance and the Fuel Rod Cannon in operation.