I just got done testing for unblockable setups, here's what I found.
First, when holding up-back, you can't block during pre-jump. If your opponent uses a move that puts you in pre-block, that will cancel pre-jump and then you can block, but you can still get hit with projectiles and the like.
Next, I learned that you can't be thrown during pre-block. If a command grab and a low come at you at the same time, just block and you won't get thrown. This would seem to diffuse the low-throw unblockables that Dime_x mentioned.
Not all moves cause pre-block. Command grabs obviously do not, because you can't block them so they need to be jumpable while holding up-back.
Finally, I learned that assists DO NOT cause pre-block. This is the important step that leads to unblockables. If the opposing point character uses a command grab and their assist uses a low, you WILL get thrown if you try to block low, and if the timing is tight enough, you WILL get hit out of your jump when you avoid the throw.
Since you have to jump to avoid the grab and you can't block anything during pre-jump, they don't even need to use a low-hitting assist, anything that hits 1 to 3 frames after the throw, during your jump startup, will break your guard.
I also tested out Mortuary Drop plus Excellebella. Sure enough, you're damned if you do and damned if you don't.
While testing different combinations, I even found out that if the assist's strike and the point character's command grab connect on the same frame, the defender STILL gets opened up. If you set up a sliding knockdown, you can call a meaty assist on your rising opponent, then time your grab to catch them on the first wake-up frame.
For a practical example, team up Cerebella with Double. When you knock your opponent down in the corner with Titan Knuckle, call Hornet Bomber meaty (the timing on this is very lenient, just make sure it's active before they wake up). Then call Merry Go-Rilla exactly as they wake up. This should lead to an unblockable, and whichever move hits, follow up with otg c.LK s.MK f.HP to reset the situation. whatever combo you like.
If Mike wanted to eliminate these setups, I would suggest this rule : when a command grab whiffs on a character in pre-jump, that character can block both high and low by holding back and can't be put into pre-block for the remainder of pre-jump (and they are also un-Excellebella-ble for the rest of that jump :^). This fits the pattern set by the unblockable protection system. It acknowledges that you made the correct defensive choice, then grants you a brief window of immunity. Also, jumping techable throws does not need to invoke this protection, just like mid attacks don't invoke unblockable protection, because they don't force one defensive option.
tl;dr Merry Go-Rilla, otg c.LK s.MK f.HP, call Hornet Bomber, repeat
Titan Knuckle, Call Hornet Bomber, Merry Go-Rilla
