Casters on the PBE right now have around 50-100 extra health, just enough that problematic waveclearers with sustained damage (Azir, Sivir, etc.) have to spend a fraction of a second extra to clear the wave, but mages whose waveclear is completely balanced (Xerath, Zilean, Karthus, Lux, Brand, etc. etc. etc.) can no longer 1-shot the casters with their max rank ability, drastically increasing the amount of time it takes for them to clear the wave (sit there doing 6-9 more auto attacks, or wait ~7+ seconds for your ability to come off cooldown.)
EDIT: Note that these changes were designed/push to PBE by Riot Repertoir, who also designed and released the Guinsoo's version yesterday.
His philosophy seems to be 'If 1, 2 champions are a problem, rather than nerfing them, find every way to indirectly ruin other champions/core gameplay functions/entire classes just to slightly nerf those 2 problem champions. Then meme about it on the boards.'
Not only this, but Zilean, specifically, is completely ruined by this change. No hyperbole - the only way he has kill pressure is because his Q, since his rework 3 years ago, has always one-shot caster creeps at max rank; he double-bombs an enemy caster creep when the enemy champion steps too close, and the first detonation kills the creep, causing both bombs to detonate instantly for a large burst on the enemy champion.
This mechanic is as core to Zilean as MF's Q bounce is to her, it's his only way of having any kill pressure outside of support (but still critical for support), and now, no matter HOW LONG the game goes, no matter how much AP you stack, your bombs do not reach the 1-shot threshold on casters.
I just don't see why they're gutting waveclear for 20-30- balanced champions to slightly perturb the waveclear of 2, maybe 3 problem champions, who are probably being reworked again anyways (Azir.)
Also, why are we not seeing any of this on S@20? No one seems to know this is even happening.
