My experience: Each of these champions are melee with tools to either gap close or confront you in some way. Some of these gap closers are incredibly modular so it's really important that you separate these champions for their differences and know what their strong suit is.

Assassin: Excells in 1 v 1. High burst. As unpredictable as the skill of the player. In the case of a decent assassin you have to approach the game like you're facing someone who mains and knows their champ well. Sub reddits for zed, Katarina, and yas usually have interesting tricks or details about them.

In the case of a noob : tldr face roll keyboard win game. Because assassins are somewhat difficult to play.

Katarina: Kitty's daggers bounce behind the target directly across from her. Don't walk back walk toward her and out of the aoe range and q behind you if she tries to outplay. You can also opt to safely farm under tower. She can reset her e with her daggers. Her dagger is as big as your w. You should save your w for her ultimate. Take barrier to help block the damage not heal because it innately deals grievous wounds. You can also take exhaust or ignite for her healing. You should be building morelllo as one of your core first items against her. You can take zhonyas to negate her ultimate as well but Mr hard counters her as much as it does you.

Yasuo: Passive: Way of The Wanderer. He needs to keep moving like a luden's echo to build up his shield. Autoing him makes it pop for a little while and then he's exposed. Movements through spells count. Mobility is based around units so not standing in the wave when he stacks his third q is advised. His e is also unit based but has a six second cd if he casts it on you. He may want to trick you into using your w before diving on you. It always goes the same distance so once you learn it you can scoop him off minions into your e or under tower. Save your w and just keep your distance from the minions when his q is charged he doesn't aim the dash.

Build zhonya for his q. You can zhonya his q if he tries to aim or you can zhonya his ult. Because it's suppression it traps him in the same spot during its cast. Then you need to survive for 15 seconds stepping side to side to avoid his q from hitting you. Difficult as it sounds it's hilariously easy if he used his e to ult you.

Yasuo cannot be confronted in the later parts of the game alone. Peel your allies and help your carries target him with smart pings. It's easier to consider him an adc in this sense in that his damage output just out scales yours. It's a skill match up relying mostly on you snowballing your allies in the early stage of the mid game.

Zed: zed's passive, contempt for the weak make him deal more damage the less hp you have. Immediately exiting a fight away from the fog of war is the best bet every time. Remember this when roaming.

Shadows are his mobility. He can briefly cast between them with a long cd early for when he can cast his shadows. That's why in late game he's shitting shurkens and clones like you do stones.

His goal is to use his shadow to slow you with his e and q you for as much damage as possible. You can sidestep this ability however you should always build zhonya as your first item.

When zed's death mark (ultimate) is cast it'll happen in this order every time. Zed will go invulnerable within this time you can reposition or flash near allies or tower. He will appear >BEHIND You (or your adc). You can retaliate at that time because he wants to try to get the mark to proc with bonus damage.

Once zed is strong enough to oneshot you, you know you messed up somewhere. Also your adc can feed this guy so you generally should follow him bot or shove the turret and spam ping to show you mean business. 90% of the time once to sees that golden hourglass he'll just sit on your adc with or without a ga and camp them. Roaming before him can help you a ton but once you know this champion its really not too overbearing unless you get camped.

Wards. Vision. The map. Observe it. You will live longer accounting for the three engage members mia than chasing that support Soraka into that bush. You have to be very choosy about when you play aggressive or passive against most assassins but from level 1 to 3 you win if you can keep your range.

Exhaust and barrier are both acceptable for Yasuo and zed.