Let me make this clear from the get-go. This is not the best build for Nemesis. This is not the build I use in serious match-ups. This is purely for boxing fun, and believe it or not, it will work if you can dodge, hence the movement speed. You stick like white to rice. Insert Leona.jpf for jet sounds.
(also my first guide, take it easy on me. More ****ty, fun builds on the way if you tell me you like this one)
This is a boxing guide. You wanna hit fast and move fast. Do I even need to explain the importance of Fatalis?
Now, in a normal build, I would not grab the attack speed shoes. But this is Cinderella Nem, the boxer. More swings brings more and quicker procs on passive and other basic attack items.
This is where my guide splits. Great survivability item. But if the enemy has anti-heals, I don't justify stacking lifesteal items. The pen and attack speed are great in any other circumstance.
Wonderful item makes you speed up, (jet time, Nem did 9/11) and gain Physical Protection while stripping it from your opponent. Combined with your ult, you will shred their defense.
Attack speed build. Low damage. How do you get that extra oomph? Strip 4% of their max health with each swing. Trust me, it's scary. Qin's gives you the damage that you are missing and allows you to rely on your boxing ability.
Now, this kinda breaks the whole "boxing" style as it boosts abilities, but the movement speed and extra damage output level it out, in my opinion. The pen further increases your ability to near true damage, while your 2 will get a little extra pow. Not a bad trade.
Bloodforge. High damage, decent lifesteal, amazing passive. Why don't I get it earlier? Too good for boxing. But at the end of your build, you are already melting people, so throwing in an extra shield, extra lifesteal, and movement speed? You become an invincible boxing machine. Who needs a team?
I can't say how excited I am for her new skill cancels. Changing her dash made her even more wonderful. Here goes!
Swift Vengeance 
The pew pew to your jet engine. Last patch implemented a time between dashes (2 seconds) in which you can take any other actions. This allows you to dash into AA, or any of your other abilities, giving you time to proc on hit effects, the slow from your other abilities, or even your shield as you engage or run away. It's truly a wonderful change.
Slice and Dice 
Your bread and butter for engaging. Haha, it's a pun. Slice and Dice. Bread. Butter. Well, I thought it was funny. *cough* Ok, then.
This is your basic engage tool to slow them down. If you need to get close, land them in it and watch them fail to run from your Mach 8 speeds. If they are chasing you (this will take practice) make a quick 180 degree spin, and land this ability (slight delay, not instant). This will allow you an upper hand in speed.
If the opponent has an escape ability, pocket Slice and Dice. Run to box them, and when they escape, ->->[AA]
This ability can also be used for clearing waves, though it is very lackluster. If possible, catch whichever group of minions you want in the middle, and angle the edge to catch the rest of the wave. Again, **** usage of the ability, but sometimes it is necessary.
Remember when this wasn't a shield, it just blocked all damage? Haha, get ****ed, that's gone. But it is still an amazing ability. The trouble is that CC instantly cancels it leaving you without the healing benefit or shield. Sucks, right?
Wrong. This is part of why you have so much movement speed. Nemesis is bad against CC. So what's my solution? Dodge.
This ability is a great way to save a fight or to discourage an enemy from attacking you. The shield only lasts two seconds. Know your opponent to know if this needs to be saved or if it is safe to pop as you engage. Combine this with Shield of Thorns and you can reflect enough damage for them to kill themselves.
Also, side note, on the anti-healing build, this can supplement for lifesteal, though very poorly.
Divine Judgement 
Now this is a real humdinger of an ability. You get to steal movement speed and protections from your opponent. Quite a lot, as well. Not to mention shredding a % of their current HP. (But this is a fun build, so your penetration doesn't let it do to much. I know, I cry every time.) While this can be used to escape a bad fight, it is one of the best abilities to engage a one on one boxing match. Need I say more? Probably, but I won't.
She hit quick
Great boxing ult
She's blind, so if you lose, just claim that they beat up a disabled person, then report them
Rough early game
Terrible wave clear
Prone to shutdown by CC
Easily killed by crits
Easily stopped by abilities that move you (i.e. Anhur's spear)
None. Just box.
Just kidding. You are going to want to let your teammates engage first if there is more than one enemy. Prioritize the squishier target, dash in on them, and land your  to allow teammates to close in or for you to close the distance. Apply your ult if you expect an actual fight. I really don't want to go in depth on teamwork, just box like a pro.
Yeah, I'm stumped here.
Wave doesn't die
Use some AA
Wave takes 2 hours to kill
(This can be fixed by a better, non-boxing guide for Nemesis but wait, what? Lame)
Box. Hit a lot. Go fast. Reflect some damage.
Bad guide, haha, did you actually read it?
Just recently started playing again, after a two year hiatus. Highest I've hit this season was Diamond, been back for about a month. I quickly dropped into Platinum (ew, I'm a low tier) after a horrendous losing streak. Please kill me.
I have a new guild called Dive Comp
If you can't tell by this guide, I enjoy doing stupid, non-meta builds and play styles. Join the clan, or the Discord, and ****post with me. It still wins games, just adds to the amusement.
If you like the guide, I am a college student, so it will take me a while to make more, but I will, upon request.
Here's my Discord. https://discord.gg/hCjv8Qc