Board Thread:Questions and Answers/@comment-26005711-20151226104253/@comment-26871105-20160714155429

Hisoka, being a sociopath who blasts his loads when faced with the thrill of combat, is alright unable to push himself to fight an opponent who are either way too inferior to himself, or that they express absolutely 0 interest in fighting him or being in his way.

It's extremely likely that Hisoka does not consider the possibility of fighting with Illumi is not really because the latter was really vastly inferior to him that he does not consider the fight anything worthy to do, but because Illumi simply gives 0 fks about the possibility of fighting Hisoka, which turns him cold and bored. That's also why the only time Hisoka when he really wondered about fighting Illumi was that he considered killing Killua so that could get Illumi riled up to actually fight him, as he knows of Illumi's obsession towards Killua. Though he seemed to have abandaned the idea for now in chase of the bigger fish that is Chrollo.

So what would really happen when Hisoka and Illumi really fight to their death and everything goes? It's actually hard to say.

Considering Hisoka got his arse kicked into "nearly" biting the dust by a handful of suiciding puppets for the most part, it can't be hard to assume that Illumi's Needleman should give him an extraordinary headache once they're onto the table; which in this scenario where this setup is complete, Illumi would most likely win. But on the other hand, if Illumi was caught off-guard by Hisoka during a say, ambush, then the position of the victor should go to Hisoka instead for obvious reasons as the needles should be pretty easily blocked by Bungie Gum if Illumi resorts to throwing them at him.

But really, we don't know, it really depends on the situation and how they would try to make the most favourable situation for themselves, and there are probably too many unsure factors to really make a final verdict in this hypothetical fight imo.