In recent history, we've seen mage changes in 8.9, jungle shifts in 8.10, and most recently marksman adjustments in 8.11. 8.12 ends this "midseason" timeframe—so named because we're in the middle of the season but no single patch was kingmade as a "Midseason" event. A few final systems changes are in this patch, but our focus has otherwise already shifted to followup. The plan between now and preseason is mainly to smooth out the rough edges and balance issues, meaning until preseason comes around, patches will be less disruptive than what you've seen over the past few months.

Back to 8.12! We're tuning down the duration of allied shield abilities and the strength of the Forbidden Idol item line with the goal of making shields fairer for enemies to play against. If you were watching PBE this patch, you also saw some item changes to help fighters carry late-game teamfights. Fighters have gotten stronger over the past few patches thanks to what's changed around them, and the landscape is still rapidly shifting. We're holding off on most of these changes until the dust clears, lest we power up a class that no longer needs the help

We'll be looking to make individual marksman changes in the coming patches, but we don't want to risk overbuffing them alongside item changes. To start, we're adding power to some core crit items before looking at individual champions too heavily.
Infinity Edge
TOTAL COST 3700 gold ⇒ 3600 gold
Stormrazor
ATTACK DAMAGE 70 ⇒ 75
STORM'S EDGE MOVEMENT SPEED AMOUNT 10% ⇒ 20%
STORM'S EDGE MOVEMENT SPEED DURATION 1.75 seconds ⇒ 0.75 seconds
Essence Reaver
Essence Reaver is performing pretty well on users who have some way to "cheat" extra basic attacks (Lucian's passive or Renekton's W, or attack resets), and thus get far more ability refreshes. We want to open Essence Reaver up to a few more champions without buffing it on the core champions, and that means giving more attack speed so that champions without bonus attacks in their kit can get more bang for their buck.
BUFF DURATION 8 seconds ⇒ 6 seconds
ATTACK SPEED 30% ⇒ 50%

These changes all went live last patch; see Ezreal and Taliyah above for a few more.
Kai'Sa
PLASMA BASE ON-HIT DAMAGE 7-12 at levels 1-16 ⇒ 4-10 at levels 1-16
PLASMA PER-STACK DAMAGE 1-9 at levels 1-17 ⇒ 1-5 at levels 1-17
PLASMA AP RATIO 0.2/0.25/0.3/0.35/0.4 (for stacks 1-5) ⇒ 0.1/0.125/0.15/0.175/0.2 (for stacks 1-5)
W - VOID SEEKER RATIO 0.45 ability power ⇒ 0.6 ability power
Pyke
BASE HEALTH REGEN 5 health per 5 seconds ⇒ 7 health per 5 seconds
BASE MANA 380 ⇒ 415
BASE ARMOR 42 ⇒ 45
BASE ATTACK DAMAGE 60 ⇒ 62
Yasuo
BASE ATTACK DAMAGE 60 ⇒ 63
Q - STEEL TEMPEST CRIT DAMAGE 150% ⇒ 180%
BUGFIX The combination of Brawler's Gloves and Infinity Edge now properly grants Yasuo 40% critical strike chance

Elise
Human and Spider form movement speed increased. Human W damage increased.

We've been watching Elise for a while, but wanted to see how she'd do with the Runic Echoes rework in 8.10 and subsequent buffs in 8.11. She's pretty far below the average Echoes jungler, so the runway's clear for direct buffs.
Base Stats
HUMAN FORM MOVEMENT SPEED 325 ⇒ 330
SPIDER FORM MOVEMENT SPEED 350 ⇒ 355
W - Volatile Spiderling
BASE DAMAGE 55/95/135/175/215 ⇒ 60/105/150/195/240

Ezreal
Armor decreased.

Ez is still running rampant after the scaling nerfs we shipped partway through last patch, so we're making it easier to boot him out of lane without letting him hit his item cost thresholds. In particular, this may leave him stuck on Tear of the Goddess (potentially not even that) without damage items for longer.
Base Stats
ARMOR 25 ⇒ 22
Mid-Patch 8.11 Updates
These went live last patch.
ATTACK DAMAGE GROWTH 3.11 ⇒ 2.5
PASSIVE - RISING SPELL FORCE ATTACK SPEED 10/12/14% per stack ⇒ 10% per stack at all levels

Kindred
Attack speed growth increased. Q attack speed increased. E damage increased.

Kindred's recently taken losses from both the Rift Scuttler changes and the Zeal item nerfs. We're building on last patch's buffs (focused on adjusting Kindred's early marks to account for the Scuttler changes) with a heavier power-up this time around.
Base Stats
ATTACK SPEED GROWTH 2.5% ⇒ 3.5%
Q - Dance of Arrows
BONUS ATTACK SPEED BUFF 10% ⇒ 25%
E - Mounting Dread
BASE DAMAGE 65/85/105/125/145 ⇒ 80/100/120/140/160

Lee Sin
W cooldown decreased. E damage increased.

Last patch's buffs didn't go far enough in bringing Lee back up from the Warding Totem changes, so we're giving him a few more buffs.
W - Safeguard / Iron Will
COOLDOWN 14 seconds ⇒ 12 seconds
E - Tempest
BASE DAMAGE 70/105/140/175/210 ⇒ 80/120/160/200/240

Poppy
Passive cooldown decreased late. Q cooldown decreased; ratio increased.

Giving Poppy a bit more oomph throughout the game, particularly with aggressive builds.
Passive - Iron Ambassador
COOLDOWN 16/13/10 seconds (at levels 1/7/13) ⇒ 16/12/8 seconds (at levels 1/7/13)
Q - Hammer Shock
COOLDOWN 9/8/7/6/5 seconds ⇒ 8/7/6/5/4 seconds
RATIO 0.8 bonus attack damage ⇒ 0.9 bonus attack damage (reminder: applies on both cast and detonation)

Rumble
W shield increased. R damage increased.

We're leaning into Rumble's lane bully strengths by making fights more favorable for him and letting him carry that lead more convincingly if he can secure it.
W - Scrap Shield
BASE SHIELD 80/110/140/170/200 ⇒ 100/130/160/190/220
SHIELD RATIO 0.4 ability power ⇒ 0.5 ability power
R - The Equalizer
MAX DAMAGE 650/925/1200 (+1.5 ability power) over 5 seconds ⇒ 700/1050/1400 (+1.75 ability power) over 5 seconds

Sejuani
Icebreaker deals less damage vs monsters but no longer has a cooldown against them. More units can be frozen. W costs less, now has AP ratios. E damage and ratio increased.

Sejuani's been bristling for a buff since her nerfs earlier in the season, so we’re making her early clear healthier and more engaging. We’re also giving her some itemization flexibility by letting her feel good about pickups with AP in their stat lines.
Passive - Fury of the North
ICEBREAKER DAMAGE VS MONSTERS 400 flat ⇒ 10-20% target's max health (max 300 against epic monsters), matching damage vs other targets
ICEBREAKER TARGETS Enemy champions and epic/large monsters ⇒ Enemy champions, epic/large/medium monsters, super minions, and siege minions (see Permafrost below)
W - Winter's Wrath
COST 80 mana ⇒ 65 mana
NEWFIRST SWING AP RATIO 0.2 ability power
NEWSECOND SWING AP RATIO 0.6 ability power
E - Permafrost
FREEZABLE TARGETS Enemy champions and epic/large monsters ⇒ Enemy champions, epic/large/medium monsters, super minions, and siege minions
REMOVEDNON-CHAMPION COOLDOWN 10/9/8 second per-unit cooldown against non-champions
DAMAGE 20/30/40/50/60 ⇒ 30/45/60/75/90
RATIO 0.3 ability power ⇒ 0.6 ability power

Taliyah
Q rocks beyond the first deal slightly less damage to champions.

When we shipped 8.11, Taliyah landed in a weak spot. We gave her a bunch of buffs partway through the patch, which overcompensated and pushed her too high. So we're reining in one of those mid-patch buffs to a more workable middle ground.
Q - Threaded Volley
CHAMPION DAMAGE 60% for rocks beyond the first ⇒ 50% for rocks beyond the first
Mid-Patch 8.11 Updates
These went live last patch.
BASE ATTACK DAMAGE 56 ⇒ 58
Q - THREADED VOLLEY DAMAGE VS CHAMPIONS 40% for rocks beyond the first ⇒ 60% for rocks beyond the first (it's now 50%—see above)
E - UNRAVELED EARTH DASH DAMAGE 35/45/55/65/75 (+0.2 ability power) ⇒ 50/60/70/80/90 (+0.3 ability power)

Yorick
Q cooldown decreased late. Mist Walkers and the Maiden now update their stats when Yorick's stats change.

With no bonus AD ratios in his kit, the Sterak's shift from granting base AD to bonus AD weakens Yorick's Trinity Force damage without increasing the impact of his abilities. (Other Sterak's/Trinity Force champions in this bonus-ratio-less position are either pretty far ahead of Yorick power-wise or have other builds to lean on.) Since this build has historically been Yorick's only good offensive choice, we're giving him some buffs to offset a nerf he has no way of sidestepping.
General
LOOK AT ME Mist Walkers and the Maiden now update their stats when Yorick's stats change
Q - Last Rites
COOLDOWN 7/6.5/6/5.5/5 seconds ⇒ 7/6.25/5.5/4.75/4 seconds

Jhin
Bugfixin'.
BUGFIX Jhin's fourth Passive - Whisper shot now overrides Stormrazor's guaranteed-crit damage modifier