Kiting is definitely not one of shadow priest's specialties, but in this case it is probably one of the only ways to do this boss.

The boss only has 1 phase, and throughout the fight, he gains a stackable buff called Burning Fury, which increases his damage dealt by 5% per stack. He stacks this once every 20 seconds so as the fight goes on, he will deal progressively more damage. He has 3 abilities, 2 of which are rather significant to the fight. The 3rd insignificant ability is the fact that he lays fire on the ground which has next to no effect on the fight since the boss is mostly kited, and even if chosen to stand in them, the fire does rather weak damage.

The first significant ability is Burning Breath. The boss will stop and spin on the spot whilst channeling a breath attack that deals rather weak damage. Take this opportunity to gain extra distance when kiting. The second significant ability is Meteor Fists. It is a 1.5 second cast that allows Koralon to gain the 15 second buff Meteor Fists, allowing him to deal 120% extra fire damage split between all targets in front of him. Soloing this boss means taking the full brunt of this damage, which is very hard to heal through when Burning Fury stacks are high. Luckily there are ways to avoid/mitigate this damage. Because of the extra kiting distance gained whilst he was channeling Burning Breath as well as casting Meteor Fists, around half of the Meteor Fists duration can be completely avoided, obviously the boss will eventually catch up and so the other half of the duration must be dealt with using cooldowns such as Dispersion, Desperate Prayer, Shadowfiend, or simply heal through if no cooldowns are available. Another way of mitigating Meteor Fist damage is by using a fire resist proc, such as the Tol Barad trinket. Having this will make healing through meteor fists a lot easier (and possibly make the fight shorter as less kiting is needed). The boss will always alternate between Burning Breath and Meteor Fists. Repeat this process until the boss dies.