What is the fastest strat for all the bosses in Ultimate mode?

As far as I can tell it's:

Ogre - Bishamon
Marcellus 1 - Bishamon
Doppel - I personally use Shippuu but I suspect Bishamon is faster
Heccuba - Shippuu
Marcellus 2 - Shippuu first phase, then Bishamon second phase
Fortinbras - I suspect Bishamon is faster since none of the weapons are upgraded, but Raizen is objectively safer and I suspect that if we level it up even once itll be faster with better DPS on him than any other weapon? However the time taken to level up Raizen to lvl 2, im not sure would wash out.

Levelling it up once wouldn't be out of the way, as long as you absorb the souls from all the bosses that drop them, and then use those souls after Marcellus 2.

Any input is appreciated.

You wouldn't really need to level up at all. You only absorb the souls if you needed health recovery and such. The whole run uses Bishamon sword without any upgrades the only exception is Heccuba.

Doppelganger / Stylado dies in 2 hits with Bishsword. The first hit should be guaranteed, however the second hit you need to fish out his attack then punish.

Use Bishsword on Marcellus 2. Punish his attacks with your ultimate move. He gets into the second phase after 2 Hits.

Yes, Fortinbras is faster on Bishsword you use regular attacks to knock him down then ultimate attack for his eye. However, if you want to play safe on knock down Shippu spam then Bishsword the eye once knocked down.

Thanks for the input/advice. I had suspected what you said to be the way, I guess I was just kinda spitballin' on some other ideas of how to handle bosses. Ill do it that way from now on, since it should in theory be a free PB.

Thank you.