Well, I am a new player, I am ~60hours into the game (if u exclude afk time). BUT WORRY NOT, I do have sufficient game played to talk to you about Yu Ji on introductory level.

Here are some record of my Yu Ji exposure.. (I love exposing myself to her- cough)

Yu Ji is an assassin class hero. Yu Ji's kit is built around quick burst damage and a skirmisher playstyle. While Yu Ji's unit are not the worst, they are not the tankiest bunch too.

Here's a video showing Yu Ji's unit against others: https://www.bilibili.com/video/BV1Q4411j7dA/?spm_id_from=333.788.recommend_more_video.18 - You start the video at 6min 30second.

Yu Ji should not be played as a direct front liner but a lurker/flanker; she has a ability that makes her invisible until certain distance (depends on enemy's vision line). An eye appearing above the enemy would mean that you are seen by that enemy. This enables Yu Ji to sneak up onto the victim of your choice before you reap their head apart from their body and uses it as your trophy or medal in this case.

As an assassin, Yu Ji is great against hero and unit that are squishy as oppose with beefy enemy or if they have lots of shields.

Pros:

• Great against Archer
  
• Great against light infantry (& also hanzo 50/50 imo, he dies if u land 3 Qs.)

Neutral:

• It is decent against medium defence hero (should do the hit and run against them, otherwise you might lose quite a few units)
  
• Decent against Cavalry hero (non range). I find this a skilled matchup, if the enemy is inexperience & alone, you can pull them down from their horses. If the enemy comes in full health with their units, you might not be able to drop him from the horse with a single caltrops. Annoying to deal with, but do-able. Personally think you should leave them to the lancers (pikeman).
  
• Against light Pike/Lance users. While you lose out to their range (unit wise), their hero might be squishy enough for you to burst down, especially if they engaged previously and not on full health.

Cons:

• Anyone tanky is your big nono, leave it to others for that job, you go for them after you clean up rest of his teammate.
  
• Anyone with a shield can parry your attacks, putting you at risk if you play too aggressively, engage (& disengage when necessary) from outer perimeter and not right into them.
  
• Range cavalry will put many holes into you before you get to them, very risky to attempt this, loses more than you win generally.

When playing Yu Ji, you want to kill, and kill and kill. You just want everyone dead. The issue is, you cannot just kill everybody, so you need to learn the maps and position well.

After looking at the pro & con of Yu Ji, you might think that.... Hey, she has more weakness than strength at this rate, why Yu Ji?

Simple, unless enemy are all tanks and range cavalry, you can still do something. You won't contribute to the frontlines by tanking, but by doing burst damage from their flank to force their hero to retreat or just out right kill them and make them regret overstaying.

Yu Ji is great on maps that archer thrives in (generally cavalry also thrive there too, but you can play around that.). When you pick Yu Ji, you either follow your archers, or you lurk around position that are prone to have an archer camping at. Another issue to look out for is that, archers are generally not alone, and has melee unit guarding it; this is when invisibility ability come into play, you can easily bypass the melee unit (not approaching through the front obviously :x) and finish the archers off. Something to pay attention to is if your units can follow through with the attack together with you. If they are not able to, you might accidentally become food for the archers.

Archer tends to be found on high ground, or behind their main force. When the battle start, approaching the high ground from the flanks is great and then rotating towards the back of enemies' frontline. You would want to approach them with invisibility at around 150-200 distance away, to ensure that they got no idea about you.

While Yu Ji is deadly with her units around, sometimes you have to let your unit buy time for you to escape after sinking their archers deep into the river. Yu Ji's secondary weapon (cross bow) is not weak. It does 200+ headshot in general, which is a good chunk of their health. Even without units, Yu Ji can play around point quicker than most units (Shadow walk give move speed). When opponent's unit are running low, you can go in for a quick burst and attempt to kill their hero.

Passive Ability:

• Master Of Subtlety: Increase stamina regeneration rate while disengaged. Yu Ji does more damage to enemy with less than 20% health.

This is what makes you an assassin and a ks master, this also increase stamina recovery when you disengage before getting your next victim

• Elite Assassin: Cooldown of Shadow Raid is reduces by 2 second when enemy hit by Blink Strike | Yu Ji's unit does extra damage to enemy with less than 20% health.

Well 2second is not a lot, but chances are you will be hitting them twice with your blink strike after using Shadow Raid, so good news is your skill is 4second quicker to refresh :)

• Solid Love: Labu Labu skill. When Yu Ji or Xiang Yu saves each other, more health will be recovered.

Hope you have a friend to pick your husbando-

Active ability:

• Blink Strike: Yuji Blinks forward while causing bleed and reduced defence to target that is hit by blink strike. Cooldown is reduced when an enemy is killed with melee attack(Gotta assume your bow won't reduce it...?). [CD: 45s]

Your bread and butter. You have to at least ensure your Blink Strike hits the enemy hero such that you can melt their disgusting defence and ensure that their health goes down to 0.
Unit ability:

• Shadow Raid: Unit charge into designated location and attack is increased for 25seconds. Using Shadow Raid refreshes Blink Strike and next Blink strike will have its cooldown removed. [CD:90s]

A great skill that give you 2 more free blink strike while also melting opponent's squishy units, bye Hanzo.

• Fire At Will: Unit fires bolt at enemy within range, each unit only fire once. [CD:30s]

Shooting once is kind of pathetic, but its a great initiator or something to chase enemy down with.

• Shadow Walk: Improve movement speed and improve concealment of Yu Ji and her units for 30second. Uses 50% camo. [CD: 10s]

• Caltrops: Yu Ji spreads caltrops on her location, once trodden upon, cause pain and reduce the targets movement speed. [CD: 120s]

Bye bye cavalry... not really, you still got to butcher the horse before he walks out of it... I wish the cooldown is more feasible... like 60s? idk 120s might as well not use it if you are not good enough to eat horses for dinner.

Basic combo:
Stab and Combo Impales is great and should make it a habit to use.
Sword dance is generally used when you Blink Strike into a ground of harmless sheep- I mean archers and you can aoe them to almost dead.

Hardened Plate

• 8 Melee
  
• 8 Attack Speed

Yu Ji's attack speed is pretty decent on its own, I would recommend melee damage. (Melee dmg scales with your Q whereas attack speed do not.)

Reinforced Plate

• 8 EXT Armour
  
• 8 HP

Yu Ji's base hp pool is pretty high (800+), which makes the increment from HP plates lower value as compared to external armour (30/34 | head/body). a 24 increase for armour is almost double in external armour.

Tempered Plate

• Shattering
  
• Penetration

While EXT/INT armour do not further reduce slash damage, Yu Ji's Stab (LMB + MB3) is piercing damage, and so is her secondary weapon, making shattering scale better as oppose to penetration armour.

Red : high chance of archer being there
Yellow: Can be found there
Green: Low chance / Seldom
Blue line: starting pathing
Brown: Maybe use invisible for 100% stealth

Sicilia:

ZhongZhou Forest:
If you have your team mate gain control of the upper half of the map (the 2 closer points) you can force the archer down from the bottom half of the map (hence the yellow X).

Xiangping Outpost:
Point C generally is where archer gains the most foothold and advantage in. If they were to venture to A... Well they either get caught by lone random cavalry or, we secure C and they have to push into it.

Xiling:
The left part of the map is great for archers as cavalry cannot insert themselves into the ruin. The highground on the right is also a prominent point for the archers, this will be 50/50 and also where part of the map your team is wanting to hold.

As your play at high rank, the games is more dynamic, and you have to play accordingly.

I started this game late and this has helped me lots:

• https://www.youtube.com/watch?v=sFlTKvmT9r8 Yu Ji Guide
  
• https://www.youtube.com/watch?v=q5il9GyawOA Plate guide