Relevant Talents used:

Body and Soul
Mindbender
Desperate Prayer
Divine Insight
Divine Star

iLvl: 501

This encounter is extremely fun and challenging to solo as a Shadow Priest with T14 gear. Of course it will become easier as we progress further in iLvl but as of T14, this boss remains challenging and fun.

The encounter is a council style fight that consists of Arcanotron, Electron, Magmatron, and Toxitron. Each have 100 energy that slowly depletes as long as the tron is active. The fight begins with only one of the trons being active (chosen at random) and once the first tron's energy depletes to 50, the second tron will activate (also chosen at random). Once the second tron's energy reaches 50, the third tron will activate. At the same time, the first tron's energy will reach 0 and thus deactivates. This way, aside from the very start of the fight, 2 trons will be active at all times.

Once a tron's energy reaches 45, it will cast a shield on himself. Attacking a tron that has this shield will cause various detrimental effects, depending on the tron. This is to discourage from continuing to DPS the old tron after a new one has activated.

Overall the encounter is quite intense as the incoming damage is quite high (it was 2 tanked back in cata). Therefore to minimize some of the incoming damage, It is sometimes ideal to kite around for a while. Kiting not only minimizes incoming melee damage, but also buys some extra time for your big cooldowns to be ready. Below are some of the tactics I used to deal with each tron.

Toxitron - Toxitron initially casts a poison cloud in the player's location. The cloud causes anyone in it to take 50% extra damage. It is ideal to position the boss in such a way that the boss himself is in the cloud but the priest isn't. However this isn't always the best idea as there will be continuous periodic kiting throughout the fight. Extra care must also be taken when the boss casts this when 2 trons are active as +50% damage taken when 2 bosses are meleeing can be deadly. Toxitron Also summons 3 adds that fixates on the player. Once it reaches the player it will explode, dealing massive damage. The trick is to get close enough for the add to explode, but not close enough to get caught in the blast radius. Since this is old content, there is a high chance that the explosion will 'miss' regardless. Summoning the adds takes 10 seconds so it is definitely recommended to kite away from him during this time.

Magmatron - This boss starts with Incineration Security Measure. Low damaging AoE. Use this chance to move away from the boss. Magmatron also fixates on you and casts Flamethrower, which also isn't very damaging. Again, this is another chance to gain some distance from the boss.

Arcanotron - Arcanotron periodically summons a Power Generator under itself. This boosts his damage by 50%. Obviously the strategy here is to kite him off the generator and stand in it yourself but, due to the constant kiting involved, it is never a good idea to stand in one location for too long. Nevertheless there are still situations where standing in it can be ideal. While using Dispersion for example, standing in the generator can provide some extra mana return. But usually the mana return and damage increase isn't really worth the effort of standing in it for 3 seconds before moving off. However care must be taken when both Arcanotron and Toxitron are active as Power Generator from Arcanotron and the poison cloud from Toxitron means your health bar can go from full to 0 in a few seconds.

Electron - Not much to say about this one. He casts a debuff on the player which requires him to run away from raid. But since we're talking about soloing here so it doesn't really apply. He also does a chain lightning that chains to 3 raid members which again doesn't really matter when soloing. There isn't really much to watch out for here.

In terms of healing, unlike Cataclysm, Flash Heal is no longer the go-to spell for heals, since it isn't spammable anymore. With the 30% nerf coming in 5.2, it makes it even more useless for healing. But nevertheless it is still an excellent tool when no other heals are available. It's not really easy to determine the main source of healing, but PW:Shield seems to be the biggest source, accounting for 22% of the healing done. In the fight, a mixture of PW:Shield, PoM, Divine Star, VE, DP, Renew, Desperate Prayer and Flash Heals were used, many of them on CD.
http://i.imgur.com/P3mS3BJ.jpg

Good luck to all priests attempting this fight, I can say it's one of the most challenging and fun soloing encounters I've had in a while. I personally prefer endurance solos rather than the ones that requires heavy DPS to beat enrage, though both are welcome.