Assassination, Tortos, and Crimson Tempest.

[Algroda]

From what I have seen on Tortos, most high ranking players are using Crimson Tempest on the bats. Due to them dying relatively quickly (so rupture dotting isn't so effective) is this what is most effective?

Quick napkin math:
FoK costs 35 energy, as do finishers, but due to Cut to the Chase finishers cost 10. For ease of math, let's assume 10% haste or 11 energy / second. If we pool to 80 before bats and bats last at least 12 seconds (best case for CT) that gives us during the 6 seconds of envenom buff a total of 80-10 (finisher) + 55 (regen) + 20 (VW, assuming 2 ticks, best case) 145 energy or 4 FoKs.

1 cast of Crimson Tempest hitting 9 targets (8 bats+Tortos)
This parse has CT hitting for 15,403 average, and ticking for 36967 over the duration, for a total of 52370 per target, or 471330 per cast. Then 50% application of DP, 9*34877*.5 = 156946. Total of 628276.
This is what Envenom then needs to beat.

Poisons have a 50% chance of application baseline, +15% during Envenom. DP was hitting for 34,877 per hit. Assuming the 15% chance averages out, that is 5232 extra per FoK. 4 FoKs, 9 targets, so 36*5232 = 188352
Envenom average hit: 197,484
6 seconds of AA: 8 hits (which is slightly over, realistic is 6 or 7) 41856
Total: 427692

Conclusion? Crimson Tempest best case beats out Envenom's best case. If bats are dying more quickly. This was more for my own numbers than to spread the word, but let me know if you see any major problems. (I ignored crit because it should equal out either way for it, as well as the initial DP application. Tossup, since CT gets in 1 second more quickly vs Envenom at +15%)

[Sesshou]

Seems like you are leaving out the ~156k expected poison damage from using CT. Though I also think that all the bats living for the full duration of CT is unlikely (but I never timed how long it takes to kill ours). You could also get more than 3 FoK off in 6 seconds if you pool before you envenom.

[Algroda]

I had 4 FoKs per envenom. However, I did mess up the way I presented it. Fixing that now.

[Koji2k11]

im speaking from my personal experience our bats didnt live long enough to CT them i mostly manage to fok 3-4 times and they die