Ok, so I've gotten around to actually labbing this and applying it to different situations, found some good things, found some not so good things.
I asked earlier about the level of safety when done from a [starter] amp db1, 4~df3 setup, and as you said d1~db4 becomes punishable, but I did find some other things because I was looking there.
@Under_The_Mayo remember my plus db4 setups? Well these are subject to the same random block advantage based on hitbox size and how far back the strep is placed. In other words, if the character doesn't have a wide hitbox, this setup goes from safe d1~db4, to very plus d1~db4 because the bug has to orbit before it hits them instead of exploding at their feet.
This is where all my headaches with the plus db4 setup are about to pay off. Instead of 1, 4~df3, we can do backdash 1, 4~df3 to place the bug farther away, while maintaining everything else about the setup. This causes the strep bugs to orbit instead of explode at the feet more reliably against more of the cast. I have thus far found it impossible to do against Sub-zero and Jacqui, but I haven't been through the whole cast.
This creates a small gap that some characters are going to be able to fatal blow through if they're mashing it depending on start up animation (Scorpion because he doesn't actually move forward until late), but we can always close that gap by not backdashing or possibly just canceling into the s1 early.
All of this also got me to try amp db1, back dash cancel 4~df3 into b34. This can also change the bug distance to make it orbit, and since they're locked in a low block for a very long time, the bug hits super late. Not sure yet because it's late and I was supposed to be asleep an hour ago, but it may make b34 plus on block, and it should also beat people trying to flawless block u2 the gap. Not sure about u3, since it might invincible right through a single strep bug.
Edit: Regarding the b34 stuff mentioned in the previous paragraph, flawless blocking doesn't work, and it looks pretty plus. Hurtboxes may wreak havoc, but it's working on Sonya as of now.
There's a lot to unpack here.
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