I'm not sure if it's a bug, I don't think it is. It's probably when the Ninpo connects fully to the glowing orb in his chest. The same happens with a DS UT when Ryu hits it. A lvl 3 Void Ninpo does the most damage, but on a first run, it's not ideal to commit to that, given the other challenges the game throws at you, like TOV 4. Or you should skip upgrading Wind Ninpo.
And the Marionettes blocking a WS is not really rare. It happens frequently enough. With bots flying around, it's better to use essence for a 360ET, since it's a guaranteed delimb and generates some iframes. Even when you have 2 essence floating with bots still around, the WS sometimes targets them. It is the preferred weapon of choice, after the bots are gone.
The DS 360ET has less reach and iframes and you need to get closer to the Marionettes than with LS or TF. And even when you use windpath OL 360ET, delimbed hooverbots will still hit you in air, OL, making the marionettes insta kill you. I managed 27 marionettes, when I got OL rocket stunned, electrified (grains), insta swirled (grains) and then killed by a second marionette spinning in from of screen. It's just very random.
I'm circling the arena, even trying to heal up by taking distance, but I'm getting chipped too often and only have so many healing options.
Doing this OLB DS lvl 3, flame ninpo lvl 2 is no joke. I beat it the first time on a new game using the same strat but with LS360 ET, which tends to be more forgiving. doing it NG+ with TF, is even more easy.
My point exactly was that killing 20 hoover bots with OLB DS is very tricky, because you get rocket spammed OL, mid combo and if you damage a bot to almost zero health, you have to be careful when to commit. The DS is just not the best weapon for them, or I'm missing a good combo(the 360Y rarely connects) . Even the lvl 3 UT has to connect every single slash, for it to kill one bot.
Beating the game OLB isn't really the problem, also not with with weapon restrictions I think, but there are some tricky areas and TOV 4 is up there and I want a good score.
I've decided to start over and going to move this thread to NGRealm.
If you always do what you always did, you'll always get what you've always gotten