DFFOO [JP][Dorgann Event][Alt Run] Vayne using with his BT/FR with Dorgann friend and Yang
9Boss is not ultra tanky, so even without pre-FR HP chipping, Vayne is still able to bring down the boss within one FR.
This is not a Dorgann showcase, it is just how normally Dorgann would behave with Vayne hoarding all the turns with his own FR, and Dorgann with character that initiates a BT phase.
I tried different iterations of a Dorgann friend run with Vayne and Cor, I would just share some insight in addition to this setting.
Why not Cor but Yang?
While Cor provides a bit more support then Yang, pairing him with a ST character (Vayne in this case, or Dorgann when he is using ST attacks) in this setting actually impedes your ability to break the targets with a "difference of time". Cor, as an AOE preemptive strike unit, technically breaks the target at the same time as your controlling character, even though Vayne's skill look like it breaks the target afterwards and regardless of who you choose.
When you try to actively use Cor with Dorgann in an active setting, such as Vayne going to BT, even should you only attack one of the targets to wait for the other to recover from break, Cor's preemptive strike would sabotage that additional break that you would normally get.
Using someone like Yang or Vayne with BT on the other hand would have no such problem, since their follow-ups come after. Dorgann would still move twice when whoever's follow-up break the recovered target.
If you use Cor with Dorgann passively and break targets "wrongly" however, the preemptive strikes should push the the target's turn away for another to come, thus netting you a gain of breaks. In that sense, Cor would be a great ally if you strategize that way.
Dorgann FR with BT phase (active use):
Honestly, it is actually quite hard to pull off the double off-turns even when you attack and break one of the bosses to let the other one recover. In the course of the whole Vayne FR I think only two additional breaks happened.
So in the end it does not look that much different from how you would use Vayne other than the extra targeting management.
Ardyn FR probably has a better effect for this since it resets enemy breaks much faster. Or one can just have Sephiroth stand there with his BT, he does not have a follow-up.
Vayne FR or Dorgann FR for the BT phase?
The dmg is actually very similar. Dorgann FR had around 80% less bonus at the end, but the dmg was somewhat compensated by the 30% cap. Vayne FR/BT edges out a little bit, but not by alot when Dorgann got 2 out of 4 turns before Vayne BT happened.
Things may be different should Dorgann be able to hoard all 4 turns beforehand.
Being designed for a testing ground for his FR, obviously had I waited for enemy FR to start to initiate my own FR, the dmg would be ridiculous, but both enemies resetting themselves to be broken every turn simply isn't something that you see in most of the fights.
Also the BT dmg in this run is just slightly more than Cor/Vayne/Kain, for reference.
Less is more?
I think maximizing his FR is much more effective with passive build ups using enemy turns, letting him hoard the FT turns or special methods like Sephiroth BT. Waiting for the enemy to recover from breaks simply takes too long and that is assuming you don't (re)break them together.
Most people just run him solo/duo and wait for the enemy to move, or boost FR bonus all the way and then call him when threshold mechanics hit you.
At bare minimum, he still functions well as a rebreaking unit with AOE off-turn capabilities. With delicate planning and execution, the skill ceiling can get very high.
P.S.
The pre-FR phase is interesting for Vayne when his partner was Cor and Selphie. Their mBRV can be raised sufficiently enough that Vayne can actually deal full dmg with his skills, completely ignoring the mBRV down aura.
With Yang though, it is not quite possible.
Considering he is not even having high innate mBRV and not a synergy character, he is actually quite good for this fight. (Do remember he actually has party auras, including mBRV outside of BT despite being mainly a rebreaker DPS)