That video was a huge help for a couple things, primarily the 2 large enemies at the end of stage 3 and the midboss on stage 4. As for scoring, the way im playing (which is quite a bit different than him) i'm still ahead of his score each step of the way.
I wasn't able to get the one up in any of my 3 runs, in fact, taking out that mid-boss in stages like that turns it from a 45 second battle to a 2 minute battle, and I end up dying anyways, so not worth it for me...yet.
Here's where I am at stage 3 boss; I usually get the extend at the beginning of stage 3:
Stage 3 boss: 163,727,048 / All 4 health (3 to start, plus extend at 100mil, not getting the 1up)
I usually die once, sometimes twice on stage 3 boss. Not sure what to do, I go back and forth between blue and overdrive red.
Stage 4 is relatively easy until the mid-boss, and he is now more manageable after watching that video. I'm still really struggling at the stage 4 boss. His first 2 forms I usually make it through, then die once or twice during his last 3 forms, need a lot of work on him.
New hi-score:
246,379,882 - mjmjr25 - Stage 4 (boss) - Seseri - Black Label