Scariest Champs When Fed.
My vote goes to
.
My vote goes to
.
especially the lolipoppy skin

If you can't instantly 100-0 him, you're pretty much just another sack of gold.
Fed = can kill anyone instantly. So the scariest is simply the one who has the highest mobility so you cannot escape their wrath...
Urgot
or
Thats like calling
or
scary when fed, good late-game scaling does not mean scary when fed early, not compared to the above anyways.

I'll vote for Akali. I have NO idea how to escape even an unfed Akali.
Anyone who snowballs ludicrously hard. Good luck even thinking about fighting them once they get 2 or 3 kills over you.

Nah Talon
http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1689035952/217730858?tab=overview
http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1688456779/217730858?tab=overview
http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1686253931/217730858?tab=overview
http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1678033461/217730858?tab=overview
mine goes to
and 
Have you ever seen an
with more than 3 early kills? most unstoppable thing iv'e ever seen.
LeBlanc, zed, fizz.
Basically, free gap closer + escape that can be used to get in and out without a meaningful delay in between. Doesn't matter if you're doing pretty well in your Lane, if they're fed and you're not an ahead tank or a super fed other role, you're going to go 100-0 as soon as you see them (because they can chase you so easily).
idk
looks pretty fed to me.....
Just lets his crows kill everyone while healing up :(