Kevin, Ryan and Neil are a Fighting-Dark-Psychic triad: a dissertation
I’ve worked in close contact with the Pokemon fandom for several years so I’m competent enough to make this statement.
First, the obvious:
Kevin is Fighting type: The Fighting type isn’t just about physical strength, it embodies virtue and honour and it is typically the “Hero” type in juxtaposition with Dark which is the “Evil” type in Japanese.
Kevin is not only canonically the strongest of the three, he’s also the most honest and honourable, as specified in the official source below.
In the Money Tree, Kevin kickstarts a series of regrettable events, however his motivations were noble: he wanted to help his friends and himself live a better life.
Even in real life, Kevin is a complete hero and role model and has never done anything wrong in his life. Kevin is Fighting type.
Ryan is Dark: First of all, Ryan hangs out in graveyards, owns several cursed items and writes creepypasta, or at least used to.
Now you may tell me that this would make him a Ghost type rather than Dark, however I beg to differ: Ghost is weak against Ghost and immune to Fighting. Ryan cannot feasibly be weak to Ghost- and in Mister Basement, Kevin knocks him out in a single move.
IF YOU THINK RYAN MURPHY: PSYCHIC FRIEND IS PROOF THAT RYAN IS PSYCHIC TYPE, THINK AGAIN. Ryan may be able to use Psychic powers but it is clearly not something that he does naturally and willingly. He may know Psychic type moves but it isn’t his bread and butter. Also, this image is really good.
Ryan is clearly the most morally ambiguous of the three. While he is on the same side as the other two, he operates by his own specific set of greyish morals. In The Vigilante, he becomes a hero archetype, however he beats people up and is shown to be a general menace.
Moreover, in The Curse of Spooky Manor, he lies to Kevin to preserve his own safety and Neil’s, a classic Dark type move. In general, Ryan is shown to use any means necessary to overcome difficulties, no matter how dirty or trope-breaking. Plus he has the Dark type aesthetic. Look at him. He has the Dark type aesthetic. Look. Ryan is Dark and there is very little contrary evidence to this statement. He may however be a mixed type, like Dark/Poison, or Dark/Fairy or something.
Neil is Psychic: Neil is often played as the geeky smart one of the trio, and also the “idea-haver”, making him a plausible Psychic type and thus nicely completing a rock-paper-scissor triangle wherein Kevin beats Ryan, Ryan beats Neil, Neil beats Kevin (not to say that they would ever fight each other or have any reason to, but this is how hypothetically the weaknesses would work out).
Neil’s videos and music have a typical Psychic type feel, implanting songs and memetic content in people’s heads and occasionally causing headaches and nausea in the least acclimated. Neil’s mind control abilities would deserve a post on their own as this is getting long.
His aesthetic is overall consistent with the Psychic type, with stats probably strongly oriented towards special attack rather than defense, as is common with Psychic types. There is a chance, again, that Neil may be a mixed type, though I feel that in his case it would be a lot harder to identify his secondary type. However there is strong evidence that he is at least part Psychic.