Tompa: I don't know how to do the trick that makes the sword cause full damage while holding it out rather than swinging it, so I haven't been able to confirm for myself whether it can be done faster. But by staying a little farther up towards the top of the room than in your WIP, so that Mothula got bounced back into my sword immediately after having its invincibility canceled on the spike traps, I've managed to score four hits in quick succession.
flagitious: Yeah, I know the Fire Rod wouldn't be useful in the TAS, I was just using it for my testing of the invincibility timer. You'd obviously want to use the sword in the actual run since it does more damage.
And three-hit combos are possible with the Fire Rod, but the only time I've managed it is when I've pinned Mothula into a corner while there are also some other moving spike traps around it. It is pretty sweet when it happens but it still wouldn't be practical in a TAS.
Edit:
Scratch that, I figured out the full damage sword trick (kind of, anyway) and made an SMV of the fight. I have zero experience with TASing, so it's not optimized at all, but it's still 8 frames faster than the fight in the WIP:
SMV link