"Hey guys! Coupled with all these other upcoming Shurima releases, we've got an update to Cassiopeia for ya. Cassiopeia has always had some really cool stuff on her kit, and we saw this as a great opportunity to polish her up and really accentuate her interesting strengths. Here’s what we’re hoping to accomplish with these changes:

1) Emphasize Cassiopeia's carry potential
Cassiopeia has always been thought of as one of the highest potential damage sources in League of Legends, so we've taken this opportunity to really push her into that niche. Alongside this is giving her a unique and powerful endgame goal-- take a look at her new passive for more information here.

2) Increase reliability
The reset mechanic on Twin Fang often feels like it doesn't work properly, even when it does. So, we’re adding a few tweaks here to make Twin Fang just a touch more reliable-- and from what we've seen, even a little bit of reliability on Cassiopeia goes a longggg way.

3) Tone down her lane bullying
Historically, when Cassiopeia has been strong, her laning was oppressive to the point of being problematic. We're looking to fix this by toning down some of her early power and making space to give her very powerful tools for the late game.

4) Channel her damage potential into her single target spell, Twin Fang
We plan on giving Cassiopeia a lot of late game power-- way too much to comfortably fit into her spammable aoe spells. Don't worry though, Noxious blast and Miasma are still going to be very important and impactful spells, but we'll be shifting some of their damage into utility so as to allow Cassiopeia better access to her E.
And with that in mind, here are the specifics:

Aspect of the Serpent (Passive)
Old passive: removed!
New passive: Cassiopeia gains a stack of Aspect of the Serpent for each second that an enemy champion is poisoned and for each poisoned unit that she kills. Her ability power is increased by 1% for every 25 stacks, up to a max of 375 stacks.
At 50 stacks, Twin Fang now heals Cassiopeia for 6/8/10/12/16 (+0.1 ability power)
At 150 stacks, Cassioepeia gains 30% CDR
At 375 stacks, the AP bonus from Aspect of the Serpent is doubled.

Noxious Blast (Q)
Provides Cassiopeia more movement speed later in the game but, in turn, deals less damage.
Damage: 70/105/140/175/210 (+0.35 ability power)
Movement speed: 10/15/20/25/30%
Cooldown: 4 seconds
Mana cost: 40/45/50/55/60
Delay increased by 0.05 seconds

Miasma (W)
Now a notably more powerful slow tool but has a higher cooldown and deals less damage.
Damage per second: 10/15/20/25/30 (+0.1 ability power)
Cooldown: 15 seconds
Mana cost: 40/50/60/70/80
Slow: 15/22.5/30/37.5/45%

Twin Fang (E)
Is now MUCH more reliable when checking for poisoned targets and has a higher AP ratio later in the game. Also, now grants mana upon killing a unit.
Damage: 55/80/105/130/155 (+0.4/0.45/0.5/0.55/0.6 ability power)
Mana cost: 30/45/60/75/90
Utility: Now refunds its mana cost plus an additional 3% of Cassiopeia's total mana when it kills a unit.
Usability: Now has additional checks in place to see if target was poisoned.

Petrifying Gaze (R)
Lower cooldown, but also slightly lower damage.
Damage: 150/250/350 (+0.5 ability power)
Cooldown: 120/110/100
And that's it. I’m sure Cassiopeia veterans out there have some concerns about some of these damage changes, so I'd like to highlight a few things.

The reliability change to Twin Fang cannot be understated
This has huge implications on her DPS potential. More E's with a higher ratio = more DPS. For anyone used to playing Cassiopeia, you'll notice a difference immediately.

Much of her kit has been restructured to make Twin Fang more accessible
30% CDR, buffed movespeed on Q, a buffed slow on W, and a lower cooldown on R all come together to make Cassiopeia's damage more readily available.
Additionally, the life on hit on Twin Fang allows Cassiopeia to stay in fights for longer periods of time, much like lifesteal does for AD carries. This means Cassiopeia will be free to do more damage over the course of a fight.

Aspect of the Serpent grants Cassiopeia significant AP in the late game
This'll help make up for some of the base damage tuning, but also simply give her more damage than ever before at full build
So! Please let us know what it feels like to play with this new passive. I’m particularly interested in the following: Does “Aspect of the Serpent” change the way you think about the laning phase while playing Cassiopeia? Does Cassiopeia feel particularly powerful in the late game as a result of her passive? How do the usability changes to Twin Fang feel?
Lastly, as with most content on the PBE, keep in mind that many aspects of Cassiopeia are still works in progress-- which means some things might look a bit weird, and others will likely be a little buggy. We’re already working on a lot of this, and we'd love to hear your feedback in case there’s anything not already on our radar.
Alright, that's all for now, but I'll be around! I hope you enjoy Cassiopeia on the PBE!"