There are three set bonuses of interest here: 2pc t12, 2pc t13 and 4pc t13.
2pc t12 - SF -cooldown, +damage.
This is the set bonus that some people occasionally use instead of our current unusual 4-piece bonus. Reduces the cooldown of Shadowfiend by 75 sec, and increases its melee damage 20%. A very solid set bonus, worth about 800 DPS from damage alone.
Also increases mana income from Shadowfiend by 45%; this may have an indirect effect on DPS, particularly on movement, AoE, or multi-DoT fights where mana becomes an issue, or if your raid asks you to de-form to heal.
2pc t13 - SW:D -backlash, +damage.
This set bonus isn't really in question; tier-13 items have more stats than tier-12 ones, and this set bonus is better than the tier-12 4-piece. Reduces SW:D backlash by 95%, and SW:D damage by 55%. This adds 816 DPS on a typical stand-and-burn fight where HP wasn't a concern.
In practice, however, the backlash protection also helps your healers, and allows you to use SW:D at times where you shouldn't've, due to low HP. Thus, in practice, the true effect is more pronounced. Also becomes more valuable on fights with adds or multiple parts, as you'll hit execute phase more often and SW:D more.
4pc t13 - SA and SF +orbs.
This is the contentious set bonus. It's unintuitive, play-style altering, hard to math out, and suffers heavily on movement fights. Grants 3 Shadow Orbs whenever Shadowy Apparitions or Shadowfiend deals damage. If you simply wear this set bonus to a stand-and-burn fight and don't even alter your rotation, it's worth 1100 DPS; slightly superior to the 2pc t12 bonus, but without the bonus mana.
You can, however, squeeze a good deal of extra damage out of this set bonus. First, some data:
This is the output from my shadow simulator, regarding different rotation options used with 4pc t13 (2 Normal, 2 Heroic). The final line of the output corresponds to 2pc Heroic t12 + 2pc Heroic t13.
The two best rotations are as follows. In both cases, it is a damage loss to delay SF to sync it up with AA, or to delay AA to sync it up with SF.
- Use MSp/MB rotation when SF is up; return to normal rotation after 2nd MB, despite that SF has 2-3 melee swings left.
- Use MSp/MB rotation when SF is up.
There are also two other things you can do you squeeze extra DPS from the set bonus.
Firstly, reforge any Haste in excess of 30% to Mastery. This was already done for the data you see above, but without it, the value of the set bonus was ~600 DPS lower.
Secondly, move unnecessarily. By raising the portion of SW:P ticks under movement, you raise the portion of MB hits under 3 orbs. Whenever you cast an instant spell, move a little bit. Assuming ~0.5 sec movement per instant spell, this adds about 500 DPS, bringing the total value of the set bonus to ~3000 DPS.
Take caution, however; you are extremely sensitive to interruption during the burst window. If you or your Shadowfiend has to move (or Dispersion, or Heroic Will, etc.) during it, you'll take a massive damage loss, potentially in the ~200-300k range for only a couple seconds of movement.
Furthermore, on multi-target fights, or fights where you're asked to heal, you will have very few Shadowfiends, as you'll not be casting MF much, and so the benefit will be reduced. On such fights, the value of this set bonus may fall well below the value of 2pc t12.
Consider switching to a 2pc t12/2pc t13 setup on fights with heavy unpredictable movement, target swaps, or mana issues, as that set bonus is better on those fights, and this bonus is worse.
Next week, fight-specific tips for Ultraxion through Madness. Also, sorry about the poor formatting again this week. Blogger don't always show formatting issues correctly until the post goes live, and my internet was out for about 24 hours.