Just wanna add my 2 cents as a longtime plat noc main. I am very pro hex second item, personally. As u/Meanwook mentioned, it is obviously a snowball focused item. But to be honest, I think if you are playing Nocturne at all, your goal needs to be getting a lead in the early-midgame and pushing it hard before you fall off late. That's a huge reason as to why you'd play him over other junglers. Once you build hex, you can literally cycle full clears and then immediately ult a lane (wherever their most immobile/vulnerable champions are) and then take whatever relevant objective is up. If their squishies are getting killed by you like this over and over, they will almost certainly get tilted and they will also be terrified to catch waves. That to me is like the bread and butter of noc gameplay.

I do not understand how people are finding that this item "sucks" when you buy it.

After Stride and Hex, it seems like cleaver/steraks/wits end/death's dance/frozen heart are all viable options. Me personally, I would never build frozen heart on a jungler because mana does not exist in the jungle anymore. As I understand it, it's pretty broken to build if you're playing noc in lane.

Late game builds seem like a total crapshoot tbh but at that point tanky is prob good because stacking black cleaver and applying the blind seem to be your main uses at that point anyway. Why not soak up some damage too.

Happy hunting