Hisoka had always been the character that loomed smiling in the background of every event within Hunter x Hunter.
So, of course, his presence is felt even in the notorious and brilliant Chimera Ant Arc.
This thesis may seem strange to readers of Hunter x Hunter or watchers of the adaptation that matters; after all, Hisoka never once makes an appearance in Chimera Ant. But that doesn’t mean his character isn’t there.
What do I mean by this?

The main characters having unusual “potential” and maturing in their capabilities over time is a common, if not universal, staple of shounen manga and anime.
So too is it in Hunter x Hunter.
So often in Hunter x Hunter one character or another will notice or even marvel over the potential for growth present in Gon and/or Killua. Remember Netero’s ball game? Remember Bisky’s training?

Hunter x Hunter, however, is one of only a select few series to take the approach it does to the main guy’s growth.
Upon reading the Chimera Ant Arc (in other words, my second experience of the story), I couldn’t help but notice the strange growth in Gon’s power. For the majority of Hunter x Hunter so far, it’s been emphasized just how weak Gon and Killua are. It’s fun to watch them stomp the noobs in Heaven’s Arena, but as soon as they meet Hisoka, all bets are off.
Consider the Phantom Troupe, the Zoldycks, Hisoka, or Genthru. All of them are far more powerful than our dynamic duo. No doubt about it, Gon and Killua are weak, and always have been. Hell, Gon even cries about it in Chimera Ant (yet another example of attention to thematic detail on the part of Togashi).
Yet when we enter Chimera Ant, Gon is able to impress and even frighten multiple characters who ought to be far more powerful than he. The first is Morel.
The second is Pitou.
Both instances have something in common: Gon is consumed by hatred and rage. Now, I’m not going to analyze in detail the way Gon’s growth in power culminates and adds to the story thematically, because frankly, that’s been done to death. But I will say that after so much mention of Gon’s potential in the series, the Chimera Ant Arc felt like the first time that bottomless well was truly being tapped. His growth was bearing real fruit. He was, ahem, ripening.

And, as anyone who’s seen the Chimera Ant Arc would understand, God damn I wish it hadn’t.
Point being, when I see the adult Gon growing to the second most powerful character in the anime and beating the third to a pulp, I can’t help but imagine the most fervent believer in Gon’s potential giggling with glee.