Nemesis S8 jungle build: Slayer of tanks, Chaser of squishys

At fisrst nemesis might feel weird build wise and abillity wise, since she isn't truly an auto-attacker like aracne or bakasura, nor is she a pure ability based assassin like fenrir or Ravana. She falls on a special category that I call auto-abilitty assassin, which is propably the main reason you don't see her as much as last season since there's not a Starter item that favor basic attack and simulteneously benefit abillity usage, and this season greatly resolves around one's starter item. Regardless Nemesis is still a fantastic assassin so long as she is build and played properly.

Nemesis employs and demands great use of both her auto attacks and her abillities. Which is why this build is split between Power and Cooldown items/Attack Speed and penetration itens. The reason you want to invest on penetration on nemesis more than in other assassins is because of a unique capacity of nemesis: due to her ultimate, nemesis is able to effortlessly damage and kill tankier characters all game long, be the solo, support or a hybrid assassin, between nemesis ultimate protection steal and the penetration built in this build, she can easily shred through tanks even better than some hunters. Also, due to the investment on abillities with power, coupled with her base high speed and huge amount of slows in her kit, nemesis makes for a fantastic squishy killer as well, like the mid laner, the adc or the enemy jungler, having high damage in her autos and abillities that allow her to close the gap between them (her 1), deal great damage and slow (2) and protection-reflection against those high damage dealing attacks they have (3). Her 3 and Her Ultimate also make nemesis surprisingly hard to kill with the built in shield-thorns that also heals nemesis and a ultimate that, if used on a tanky character, also makes nemesis temporalily tanky, catching the damage dealers by surprise at how little damage they're doing to her

You'll wanna rank up Slice and Dice first for the jungle clear as well as it is your more consistant damage dealing ability, which is also the abillity you should rank up to the max first
You should rank up second Swift Vengeance since it's you getaway and chasing abillity, as well as it helps clearing the jungle a little. It is however the abilitty you rank up to max last since it would only increase the damage that this abilitty does which is generally not as relevant as the rest of her abillities.
At either level 3 or 4 you should get Retribution, 3 if you're in constant PVP scenarios, otherwise rank it at level 4 since ranking up Slice and dice is better for jungle clearing. It's the abillity you should rank up second since it increases the shield health and, therefore, increases the amount of damage reflected at the target and the heal that namesis will get from it.
You ultimate Divine Judgement should be ranked up every time you can since it will increase the slow effect on the enemy and also increase your movement speed buff, making scaping her even more unlikely