The problem with Cassiopeia indepth by a Cassiopeia Main since release.
Her whole kit was designd around her passiv. She had a spamm Style in her kit which was only allowed because her manacost got lowerd due her passiv.
This made her a good early&Mid Kite&Poke Mage while still beeing viable in the lategame if she was good enough to land a few risky Q´s and had the perfect kiting skills to outplay opponents in the lategame.
That made her a really fun but difficult champion to learn with a completly unique kit.
Cassiopeia mains were rare but were a highly respected playerbase due them having to practice way more then other Champs because they had to learn how to kite a ADC with 2.0 Attackspeed while still landing all of her skillshots like a mage.
The Rework was there to limit her early Poke and Midgame powerspike and push it more into the lategame while giving her stacks that increased her lategame dmg and lowerd her early pressure.
What went wrong?
They shifted 90% of her Dmg onto her E and took a gigantic chunk out of her Q and W importance.
They deleted her Mana-Management Passiv which allowd a good Cassiopeia Main to control her manacosts.
What did the Playerbase of Cassiopeia mains liked about her?
Her early&Midgame Power, her unique Lane-Control with her Poisons and for the high skilled Players her lategame kiting potential.
The Rework was a big fail. The whole Cass Community hates her rework until today. The Dev´s are saying that the Cassiopeia Rework was a failure too.
The Reworks were directed to outdated Champions with outdated kits, which Cassiopeia´s kit wasnt. They reworked only half of her Kit because the Dev´s had no real idea about her and still after a gigantic wave of negativ feedback pushed it live.
They tryd to buff her with numbers which "worked" but only in Winrate because she had unbalanced numbers. Even with a 54% Winrate the Playerbase was still angry, not because the Champ wasnt powerfull enough... no... they didnt like what they did to the Gameplay-feeling that they changed.
The Passiv feels really boring. Because of the missing Manacost Passiv, she goes OOM with her new only E priorized style REALLY quickly.
She has BY FAR the most linear Itembuild, which was forced by the Passiv. lets have a look at that shall we?
OK!
- You need to have at least 1 Manapool Item -> Pick One -> (
/
) - Because of the nerfed AP Ratios and her % AP buffing Passiv you need to get
(which´s interactions-math with 500Stacks got also nerfed ) - Like almost every Mage and exspecially a "Late Game" Champ like reworked Cass needs

because of the CD nerfs to W after the rework to be able to kite effectivly
Everyone needs Boots and it helps you in the earlygame with flat pen and MS for kiting,chasing and dodging.- This is the only "Free" Item-Slot but you have to use it based on the Enemy-Team sadly.
Against High HP Tanks ->
Against Heavy AP Dmg ->
Against Heavy AD Dmg -> 
When before the Rework you had a large amount of possible Items which all worked in different ways.
Fun Fact -> Statistics show that a Cassiopeia gains roughly 12k Gold in a Game which is a really low amount because that means she is only able to finish 3 Full items and her Boots, which means most of the time she cant even get to her "Powerspike" which raises her Winration btw after 40+ Minutes to a flipping 50,25% - 50,50% which shows that her "OP Lategame" has almost no influence at all.
So, what do we have today?
- A boring Kit ( playing as and playing against ) which focuses only on one On-Hit Spam Spell.
- Two timers which work together and are gates based on how soon you hit 500 Stacks and have your full Items, which is even harder because of the latest changes that end games around 10-15 minutes earlier.
- An extremely fragile Early&Mid for the exchange of a "good" late when your Team peels you enough and carrys you trough the first 25 minutes.
- Being called a "noob spam no skill" Champ... when before the update she was one of the most skillfull champs in the whole game.
- 46% Winrate which is continuously falling after all the nerfs although having the biggest amount of Scripters out of all Champs which distorts the number positively, making the true number even far worse.
- Her Passiv is hands down useless for her because of the nerfs which makes it sound good, but is worse and a lackluster and I will explain why.
25% CDR has almost no use for her.
They increased both her Q and W CD so there is no point in it, which makes it a lackluster and there are no items atm which gets her to 40% CDR without capping which steals her a lot of Items.
The only good thing is that you have your Ult more often which you already had after buying
which you cant buy anymore.
Her incredible 0.06 AP Ratio Heal ONLY on E with 6 / 8 / 10 / 12 / 16 Flat heal... which are incredible bad numbers ( 76HP with 1k AP ).
And her Manasustain is by far the biggest joke atm.
1,5% Mana refund when killing an Enemy with E.
You need to kill 4+ Minions with E to REFUND the mana you had to use to poison them with lvl 1 Q.
And 7+ when you used W to poison them.
Let alone that you most likely cant kill 4+ Minions with only 1 Q and you waste mana when using W because a normal Minionwave is only 6 minions and even with a canonwave you dont refund 100% and wont be able to farm the whole wave until Midgame.
And then... her INCREDIBLE % BONUS AP!!!!!1!1!1!
Yeah, would have been incredible if they didn´t slaughter her Ap Ratios so she HAS to stack AP or she deals no dmg and her Dmg is worse then the old one UNTIL you reached Fullbuild, with 500 Stacks, then your E deals around 180 more Paper-Dmg with your E.
And this numbers gets even lower because in the Lategame, the Enemy´s will have at least 1+ MR Items which lowers the Dmg even further to be irrelevant.
7. A Kit which completely revolves around her "Late Game Powerspike" which like already said, puts her on a 50,25% Winrate after the 40min+ mark, which clearly shows that it has a way to little impact for an unforgiving 40mins.
The Devs says that Cassiopeia was only a half-reworked because they had no idea how to complete it. Her 1 Side is her unfitting Passiv and the other one are her classic Spells.
The Rework got Cassiopeia almost no new Players, lost her a gigantic mass of her Mains she used to have, has a Kit which is anoying to play and anoying to play against AND while having an annoying Gameplay for both sides, no Playerbase she even has a dreadfull low Winratio.
If you want to test it yourself, search for the 50-100 Last Threads about Cassiopeia. They are only about Rework ideas because she´s just a bad champ right now.
It would be the best for her that her reworks gets reverted until they have a more thought trough Rework which, she really doesnt need anyways. And maybe, they use someone who doesn´t ignore all the feedback and then wents missing for 6 MONTHS . Which was extremely disrespectfull.
They basicly did a reverted Poppy Rework.
Poppy got reworkd because her Early and Mid was trash but her Late was incredibly strong.
Cassiopeia got exacly the opposite.... trashy early/Mid with a (not so) powerful lategame.
And its only normal that the community hates it.

. I rarely purchase those now because the passive provides enough CDR. You are missing items like
that are great for healing and small amounts of CDR as well as
for additional burst and movement speed. She has the same items to choose from as any AP mid laner. I don't buy
is
and maybe
(she got nothing but nerfs since release) and
(they will never remember him) also let's not forget some honorable mentions like
(he now just rift limps)
(she was nerfed to the ground just barely got back)
(rework was just a nerf as well)
(reworked then nerfed hard)
(rework was nerf passive is almost worthless and has a borderline none existent player base)
(he is doomed to be ignored maybe a good thing might ruin him like cass)
The biggest thing that needs to go with this "new" cass is her passive it has to go its holding her back.Also her twin fangs either needs to be changed so its not the focus or just remove it entirely since riot clearly can't handle letting it stay.
Every single thing you have wrote was exactly what needed to be said i wish riot had at least half the intelligence you had since time has shown us they are clearly idiotic.As seen by these cases