Other Theories
(I do not own these images, nor do I own Hunter X Hunter. These are a set of theories I have, take them as seriously as you wish!)
These are theories that I have but not much evidence for or are just silly.
Pariston is Gyro and an excommunicated member of the Spider. Also he is using Kurapika as a weapon against them. The reason I think this is because one, we know nothing of his past and it would be well within his character to play multiple sides and the guy dresses like a prince. Then Mr Togashi does say that it is Gyro's goal to spread evil, which Pariston seems to do while having fun. Also you know that there's a bottomless pit, a void of darkness in his happy-go-lucky eyes. Which would provide Welfin with a tragedy ahead of him.
Now on the topic of Pariston being an excommunicated member of the Spider, this is what I think was an interesting theory but it would give him a reason to have some involvement in the extermination of the Kurta, such as telling Chrollo their location, mainly because I think he always knew that the man wanted to get his hands on the Scarlet Eyes. This would give him the opportunity to save one of them to use as a weapon against the Spider and he chose Kurapika and manipulated him so that he would be in the position to get out long enough for him to survive.
Chrollo is a secret Kurta unknown to him. Also when he finally understands himself everyone will be in danger. The reason is we have never seen him get to the emotional point that would activate the Scarlet eyes and both men have similar features. Not to mention Mr Togashi does like to put his characters in situations that challenge them in order to make them grow and revealing this to Kurapika world cause this kind of growth. Also this would put Kurapika in the position would mean that killing Chrollo would also mean that he would be having to kill the last living Kurta.
Then on the topic of Chrollo understanding himself will lead to something bad. The reason this is because Mr Togashi is great at creating tension and subverting expectations (in the good way GOT S8) such as the Adult Gon moment. Yet he also places in enough clues to see the twist coming, if you were paying attention. Which is why I think that Mr Togashi brought up his ideology and the fact that he can't understand himself without it paying off later. As we all know, when he pays things off usually it is completely shocking and he does it well.
Mr Togashi is teasing us with a reveal of Hisoka's downstairs or his true measurements down there. This is because there have been three Hisoka nude scenes, one in Heaven's Arena energy we saw his upper body, the next, also Heaven's Arena where we saw his entire break and the last in a river in Greed Island where we saw all but his jewels.
There will be an anti-Phantom Troupe that will be formed, just think of Hunter X Hunter's answer or equivalency of the Order Of The Phoenix or Dumbledor's Army. The reason is because Mr Togashi seemed to have created a group of people who have it out for the Phantom Troupe and I would find it an interesting idea.
Even though Chrolo and Kurapika will be killed along with two more, some of the Spider will live on. This is because of the prophecy about the victory of the Spider even though their limbs will be cut in half which means that half of the support will be killed in their great battle, however due to the ideology of the Phantom Troupe, in that all limbs are replaceable. Such as the fact that anyone who kills a Spider can qualify to become a Spider. However if there is a vacancy it will be up to Chollo to replace them, yet even he has put it in place that if he is killed then one of the Spider can replace him. So even if one Spider survives then the Phantom Troupe will live on. Which I think the prophecy means this will happen and put Chrollo at ease about his death.
Greed Island is foreshadowing the events of the Dark Continent. The reason I think that this is because in the beginning of the Greed Island Arc Gon wanted to go to Greed Island but was rejected because his nen was not at the point that would allow him to qualify for the mission. He also couldn't prove he was a professional hunter because he pawned his license off in the previous arc. Yet when Gon wanted to get to the Dark Continent he couldn't because he couldn't use nen anymore, because he traded that in to kill Pitou. Yet this had a hopeful side (sort of) which could mean that Gon will be able to get the usage of his nen back and he will be stronger than he was. I also think that the events will play out similarly to Greed Island but in a much bigger way.
These are the theories I have at the moment. As Hunter X Hunter goes on I will have more. I just wanted them to get out there so maybe others could look at them and see if there are more pieces of evidence for or against these theories. Thank you for your time and reading and sharing them.