Lethality vs percent armor pen

Lethality is flat armor pen. It subtracts a fixed amount, 15 or 18 per item on the current patch, from the target's armor. Percent pen removes a share of whatever armor the target has: Serylda's Grudge and Lord Dominik's are 35%, Mortal Reminder is 30%. So lethality is at its best against low armor targets like supports and mages, and percent pen gets stronger the more armor the enemy stacks.

Drag both sliders. One item is 15 to 18 lethality, a full three-item lethality build sits around 55. The bars show how much of a 1,000 damage physical rotation actually lands.

This is why full lethality melts a support and bounces off a Malphite, and why the Zed scenario in the trainer buys Serylda's Grudge into an armor stack.

The armor pipeline, in order

The game applies armor math in a fixed order: armor reduction first (Black Cleaver, 6% per stack up to 30%), then percent pen, then flat pen (lethality). Reduction changes the target itself, so your whole team benefits from it. Penetration only exists for your own hits.

Worked example on a 250 armor tank, using current patch numbers:

Damage taken goes from 29% to 51%, a 79% increase, and the Cleaver step also applies to your team's other four damage dealers. This is why a Cleaver bruiser plus a percent pen carry melt frontlines that shrug off either one alone: reduction and penetration multiply, they don't compete.

Flat vs percent magic pen

Same idea on the magic side. Sorcerer's Shoes (12) and Shadowflame or Stormsurge (15) are flat pen: against a squishy with 30 base MR they remove most of it, which is close to dealing true damage. Void Staff is 40% percent pen: against a tank stacking MR it removes a chunk that flat pen barely dents.

Numbers are the share of your damage that lands. Flat pen wins against squishies, percent pen wins against resists. Buy in that order: flat early when everyone is squishy, percent when their tanks come online.

Grievous Wounds

Anti-heal is a 40% healing cut that only exists on targets you are actively hitting. It is not a stat you own, it is a debuff you apply. Two consequences follow from that.

First: it should be bought by whoever hits the healing target most, not by whoever has spare gold. Second: the cheap component applies the identical 40%, so buying Executioner's Calling or Oblivion Orb early beats saving for the finished item.

By class: Executioner's line for marksmen, Oblivion Orb line for mages, Chempunk Chainsword for fighters, Bramble Vest for tanks getting attacked by lifestealers.

Burns, slows, and hard CC

Burns punish HP stacking. Liandry's Torment burns for 2% of your max health per second, so a bigger health bar feeds it a bigger number. Warmog's and Heartsteel make the burn larger, not smaller. The answer is magic resist, which reduces the burn directly, plus fights short enough that the burn stops reapplying.

Slows are damage enablers. A slowed target eats more hits, which is why Randuin's active, Stridebreaker, and Blade of the Ruined King buy real output without a damage stat on the tooltip. Attack speed slows like Frozen Heart's aura cut an on-hit carry's output in a way armor can't, which is why the trainer's Malphite scenario answers Vayne with a slow instead of a fourth armor item. Dead Man's Plate reduces incoming slows by 15%, and tenacity shortens how long a slow lasts but not how strong it is.

Hard CC has a strict removal list. Tenacity (Mercury's Treads 30%, Sterak's Gage 20%, Elixir of Iron 25%) shortens stuns, roots, taunts, fears, and charms. Quicksilver Sash and Mercurial Scimitar remove everything except knockups, and that includes suppression like Malzahar and Warwick ults. Mikael's Blessing and Cleanse do not touch suppression. Nothing shortens, removes, or resists a knockup: against Malphite and Yasuo, tenacity boots answer nothing, and the real outs are spacing, a spell shield, or stasis.

Armor vs health

Effective HP against physical damage is roughly HP times (1 + armor / 100). 2,000 HP with 100 armor takes 4,000 physical damage to kill. The same math holds for MR against magic.

Resists beat HP when one damage type dominates. HP beats resists when the damage is mixed. The exception: percent max health and true damage, like Vayne's Silver Bolts, punish HP stacking because your health bar grows and theirs effectively doesn't. Against those, slow the attacker or kill them. The Malphite scenario in the trainer is this exact situation.

Ability haste is linear

Old cooldown reduction got more valuable per point the more you stacked, which is why it had to be capped. Ability haste is the fixed version: every point adds the same 1% more casts. 50 haste is 50% more casts over a fight, 100 haste is double casts. No cap, no breakpoints to memorize.

The practical read: haste is a damage-over-time stat, so it belongs on champions who cast in rotations, like battlemages, spam junglers, and cooldown-bound supports. Burst assassins usually get more from raw damage, because their target is dead or gone before a second rotation exists.

What each class does at each item count

Two practical readings. The enemy assassin hits peak at two items: that is the moment to stop walking alone, not after they show you why. And a crit marksman at two items looks beatable right up until the third completes, so the fight you force should happen before it does.

The wallet clock

A laner farming decently earns roughly 250 to 300 gold a minute: passive income is about 120, a full minion wave about 125, and plates, kills and objectives sit on top. So a 3,000 gold item completes after roughly 10 to 12 minutes of clean play, faster for whoever is winning.

That makes the tab screen a forecast, not just a scoreboard. CS plus kills tells you approximately what they can afford:

The rule that falls out: force fights and objectives in the window where your side's items exist and theirs don't. Waiting five minutes to "group when ready" usually means fighting exactly when their carry finishes the bigger item.