Okay... After a little more digging, this chain kills bowser starting at 33%. Seems like a fairly small jump when comparing his and mario's weight, but considering how small the difference in kill percents is on the Uair-Rest, plus how much more lenient the spacing is with bowser, it's understandable.
Come to think of it, the only one who can feasibly survive this by any stretch of the imagination is Dedede, due to his combination of falls peer and weight. Though, he still dies if the combo starts at 53%.... Anyone else is gone at 40% or lower, heck, a Jiggypuff ditto is out at 13%.
(By the way...for those who aren't confident in the rest hit, which I know I'm not, you can much more easily follow it up with nair or another pound.)