you would be able to land it on any character by just charging the reverse fsmash and releasing it at the right point during the bthrow animation, but it would have reduced knockback since you're smashing them out of a grab as opposed to when the grab actually releases them.
on the bigger characters you literally just hit back on the cstick and it's guaranteed (at least on falcon and ganon)
TESTED:
works on these characters (from 0%, it only works on a few at higher percents):
ganon, falcon, dk, yoshi, peach, bowser, luigi, Ice climbers, and samus
so it's weight based, size doesn't actually matter at all.
you can do it at kill percent on these characters:
ganon, falcon, dk, yoshi, bowser, samus
Luigi only works at 0%
peach works twice from 0% (it ends up being like 33% total if unstale)
ICs works until like 30%, BUT, if you hit nana with the bthrow, it looks like it works at any percent.
You could probably do it for a little longer on nana, since nana is slightly heavier than popo
----
here's the bthrow handoff I was talking about:
https://www.youtube.com/watch?v=KjkAjLtPj48
I think it might work on dk too. Maybe some other characters. I'll test later. The timing is weird.
---
another funny thing I discovered was that if you input a dash with nana when you bthrow, she gets pushed the wrong direction. It's super pronounced with bowser and dk in particular. With bowser and dk if you do this, then hit down and then neutral b, at low percents it auto-iceblock resets them because they will travel the same speed as an iceblock and land on it. they can sdi out of it, but its still super funny.
at low percent, bthrow usmash also works on bowser. It works on ganon and falcon if they di in.
bthrow fair works on the heavy characters as well. excluding falcon after mid-percent unless he DIs in.
Seems to work on all the heavys until 150%ish and then only works if they hold in.
bthrow->bair is a lot more legit and is more guaranteed and more likely to kill than bthrow fair.
I landed bthrow->nair as well. It seems a lot more DI dependent. on falcon it seems like you can only hit him during the throw animation, so it wont knock him out of the throw. More reliable at low percent, and leads to funny combos though.
I also cged bowser, dk, yoshi, falcon and ganon, with bthrow->nanadair->dash grab until kill percent. it might be an infinite. seems like it'd be easy to DI out of though. You have a very small window to regrab, and if you input it too quickly, you'll lightshield.
I landed it twice on falco while nana was positioned behind me.