After a bit of thought, I think it’s gonna be Who’s Who. Reason being that out of all of the calamities the two that would probably get under the All Stars’ skins the most, so much so that an all star would want to personally fck them up are the cocky ones, namely Who’s Who & Sasaki.
If I had to pick between the two then I’d say Who’s Who coz 1.) he seems the more motivated of the two. 2.) If Queen heard Who’s Who’s disrespectful remarks about him a few chapters ago (i.e. the if Queen dies tonight ting) then it make sense why Queen has suddenly decided to erase him from existence lolz. The word queen used ‘choudo’ gives off a nuance of it being something he only decided to do very recently.
But yh. I’m not really sure how the challenge system works but if only one Tobi Toppo will be getting a shot at the all stars it’d most likely be Who’s Who and regardless of who Who’s Who decides to challenge, I think Queen will most likely volunteer to fight him.