There are plenty of sizable nerfs this patch, and a handful of small buffs.
Snip and thread through your enemies with Gwen, the Hallowed Seamstress and her abilities!
(Q) Bandage Toss Mana Cost reduced by 20 at all ranks - 50/55/60/65/70 -> 30/35/40/45/50.
(E) Tantrum has Cooldown reduced by one second at all ranks, which should aid the Sad Mummy's clear.
(R) Enchanted Crystal Arrow has Cooldown reduced, which will allow her to make more plays and find more engages - 100/90/80 -> 100/80/60
(E) Unbreakable Cooldown reduced by two seconds at every rank, and (R) Glacial Fissure knock-up increased later by half a second.
Braum is already in a comfortable spot, so this might help to bring him more into the spotlight; especially when paired with Ashe.
Hecarim has been galloping all over the scene recently, so his (E) Devastating Charge is having the movement speed cap lowered by 10%
Kindred is having her (Q) Dance of Arrows' damage ration increased by 10%, so will now scale off of 75% AD, as well as (E) Mounting Dread's Cooldown decreased by two seconds at all ranks.
The changes are sizable, and will likely spike his pick rate, but it currently all comes down to his (E) Mourning Mist which has been made more satisfying and effective.
Marked enemies and large monsters will continuously Awaken nearby graves (up to the maximum of four). Mist Walkers will now deal 200% damage when they leap to Marked targets.
The ability will now cast at maximum range if targeting outside of range; instead of Yorick walking to the target range.
Lissandra - (Q) Ice Shard base damage increased by 10 at all ranks.
Mordekaiser - (Q) Obliterate has damage against isolated enemies increased by 10% at all ranks.
Teemo - (Passive) Guerilla Warfare will now grant the Attack Speed buff for five seconds, up from three seconds. The on-hit damage from (E) Toxic Shot is also being increased - 10/20/30/40/50 -> 11/22/33/44/55
Varus - Base Attack Damage growth going up by 0.4. Likely not a huge change, but might be enough to bring up in line with other Marksmen.
Yasuo - Similar to Varus, Attack Damage growth increased by 0.7 to help him recover from recent item nerfs and changes.
Alistar - (Q) Pulverise base damage decreased later, and (E) Trample empowered basic attack damage reduced at all levels.
Ivern - (E) Triggerseed base damage reduced mid-late game.
Kai'Sa - (R) Killer Instinct Cooldown increased at early ranks, this should reduce her engage follow up at early levels and help opponents to fight her in lane.
Rell - (E) Attract and Repel is having the stun duration cut by a quarter of a second. It doesn't feel like much, but it does reduce her more reliable Crowd Control.
Thresh - (W) Dark Passage base shield is being reduced at later levels.
Tristana - base Attack Damage is being reduced by two. Not a lot, but that was enough to know Caitlyn out of the meta.
Udyr - In the same way as Tristana, Udyr is also getting two knocked off his base Attack Damage.
The few Item changes are more small tweaks to address overuse, Everfrost had too much damage along with its lockdown power; so the damage is being reduced as well as a slight Cooldown increase.
Lord Dominik's Regard was being overused as a second purchase, so increasing the price and decreasing the Attack Damage should make it more specific for when taking on Tanky Champions; where you'd purchase it for the passive rather than the stats.
Serylda's Grudge is having the price reduced, with the idea to make it more accessible to Assassins.
Turbo Chemtank has been a little too turbo, so the Supercharge Movement Speed bonus is being reduced to 60%, but the Slow is being increased to 50%. It won't be as super speedy, but will act as a slightly stronger engage tool now.
Last, but by no means least, is the Trinity Force changes. Some Attack Speed is being exchanged for some Attack Damage, making it more suitable for more Bruisers. The Passive now stacks on Towers, making it even better for the regular split-pushing Champions. The Mythic Passive is being replaced, now granting 3 Attack Damage, 3 Movement Speed, and 3 Ability Haste.
And, of course, we're getting the Space Groove skins and event this patch!