Anyone who opposes Kefka is killed. He burns down their entire town from his tower with the Light of Judgment.
The Light of Judgment (裁きの光, Sabaki no Hikari?) in Final Fantasy VI is the destructive ray of energy sent down by Kefka Palazzo from atop his tower onto towns which he feels are resisting him, or when he's bored. The Light is a destructive beam of light cutting a path of flame into the ground, and it is implied the light creates or summons monsters to wreak more havoc. When not in use, the Light of Judgment appears as four white orbs of light that move up and down near Kefka, with one pair moving down a long path and the other pair moving a shorter path.
Kefka turned the Light of Judgment on Mobliz, Narshe, and South Figaro sometime prior to Celes Chere awakening a year after the end of the world. Mobliz's adults were killed protecting their children and half the town was destroyed, while Narshe's citizens either perished or fled, leaving the town abandoned and plagued by monsters. South Figaro's citizens largely survived and rebuilt the town. Kefka later turns the Light on Tzen, destroying the mansion of a wealthy family.
During the party's confrontation with him, Kefka has the Light of Judgment in an inactive position. After the party rejects his nihilistic plans, Kefka turns the Light of Judgment onto the planet intending to kill everyone. No specific target or casualties are shown, however.
A light comes from the heavens, cleansing all in its wake.
Kefka's EX Burst, Warring Triad, may finish with him casting Light of Judgment, a pillar of destructive golden light that hits the enemy from above and explodes on them, assuming the player memorizes and repeats the displayed button commands successfully. When using the attack, Kefka yells that the attack is "filling [Kefka] up!" before firing it via a motion of his arm. Otherwise, Kefka uses the weaker Forsaken attack.
Although Light of Judgment is never used in gameplay or seen, it is indirectly alluded to when Kefka destroys a simulacrum of Rabanastre, blasting the place to rubble out of boredom in a similar manner to his frequent use of the Light of Judgment in Final Fantasy VI.
One of Kefka's cards can use Light of Judgment as an ability. For the discard of a Kefka card, Light of Judgment Breaks all Forwards other than Kefka. It can only be used when he has more than 12,000 power.