About Cassiopeia...
In my opinion, Cassiopeia is slowly turning into what you did to Evelynn after you severely gutted her a few seasons ago, to the point where you were reported for playing her. She's barely relevant in laning phase where you can only farm and pray you don't get ganked or die, because if you do, you might as well just leave the game and not weigh down your team.
If Cass doesn't get ahead, she's just a stun bot then fodder for the enemy team, especially with the gutting of her passive hampering her powerspikes. Her E is meant to be spammed sure, but you can only cast four or five Twin Fangs until you completely drain yourself of your mana and become an open target for retaliation.
You admitted yourselves that Cass is an extremely bad spot but...it just seems you're ignoring her presence entirely.
I feel like something as small as gaining x amount of passive stacks upon assisting or killing an enemy champion (maybe less stacks if it's an assist). It'd certainly be helpful, and allows her to hopefully gain back some relevance should she fall behind in a game.
Edit:
As I thought about other possible changes, you could make Cass less reliant on E, and instead give more possible combinations.
Here's what I'm thinking: Cass' Q does poison damage over time. However, should she strike a poisoned enemy with her E, they will receive all of the DoT damage in one instance. Her Q's poison also no longer resets her E's cooldown.
Cass' W would allow her to do what she does now, if you're hit by Miasma, Cass can repeatedly cast E as long as you're in the Miasma field.
Of course, there's dozens of other ideas, but I just thought these would also be interesting.
. My opinion is to give complete rework on the snake lady. But since nowadays every rework ends up destroying
or breaking 
a champion, i think she's fine where she is.
, followed by 
. After this, a defensive item is typically needed for maximum poke. 
into 
for AP and 
into 
for AD. 
into 
and/or 
are next. 
when near 750 stacks. 
for maximum penetration (I see what I did there). Her passive gives the Rabadon buff, so it isn't truly needed. Overall, with these items and runes, I will get right around 100 armor and magic resist, 2,000-2,500 health depending on level, 42% penetration, 44 straight penetration after that, and another 20 reduced with Abyssal when I'm in range of my E. Those items make her tankier, and also will take 200 MR down to 52 MR. At 200 MR you are doing 33% of your damage after reduction. At 52 MR I am doing 65% damage after reductions. This effectively doubles my damage. Sure Rabadon's gives you insane AP, but considering her AP ratios are not that high, pure penetration works better. At 110 MR or less, you are dealing true damage on all abilities. The bonus poison damage after landing some E's will make a tank just shred health, especially with Liandry's, and your ult, Zhonya's, plus the added tankiness from items can save you from assassins.
