Lethality and penetration in League of Legends, explained

Lethality is just flat armor penetration under a different name — since patch 14.1 it converts 1:1 into armor penetration at every level, no scaling attached. What decides whether your build actually cuts through a target isn't which of these stats you buy, but the order the game applies them in, and that order is the same for every game and never shown to you.

Lethality: penetration that used to do math for you

Lethality only exists on items — Youmuu's Ghostblade, Duskblade of Draktharr, Prowler's Claw — and it used to convert into armor penetration based on level (first the target's, later the user's), which meant the same 18 Lethality on the tooltip was worth a different amount depending on who was fighting whom. Patch 14.1 removed that: Lethality now grants its full value as flat armor penetration at every level, and Riot kept the separate name on purpose, to signal that it's the flat kind — most useful against squishy, low-armor targets — rather than the percent kind, which scales up against tanks.

Flat and percent penetration apply in a fixed order

The game runs through four steps, in this exact sequence, before it decides how much armor or magic resist a hit actually goes through: flat resistance reduction (a debuff, not an item stat), then percent resistance reduction, then percent penetration, and only last, flat penetration — Lethality for armor, flat magic penetration for the rare items and runes that grant it. Because percent penetration is applied before flat penetration, and works on whatever resistance is left after every reduction, it matters more the higher the enemy's resistance already is; flat penetration matters more against targets who have little resistance to begin with. Neither one does anything once the target's armor or magic resist is at zero or below — there's nothing left to penetrate.

This is also why stacking runes and items that both grant percent penetration doesn't add up the way it looks: percent sources multiply together rather than summing, so 30% and 20% percent armor penetration don't make 50% — they leave the target at 56% of their armor, which is a smaller gain than the raw numbers suggest.

Omnivamp isn't life steal, and life steal isn't spell vamp

These three heal off damage you deal, but off different damage, and that's the whole distinction:

• Life steal (sometimes called physical vamp) heals only off physical damage, and mostly off basic attacks.
• Spell vamp heals only off ability damage, and drops to a third of its normal value on area-of-effect abilities.
• Omnivamp heals off physical, magic, and true damage combined, from both attacks and abilities — it's the newer, universal version, which is why it costs more per point on items like Bloodthirster or Riftmaker.

All three heal off damage after resistances have already reduced it, none of them benefit from heal-and-shield-power boosts like Spirit Visage, and omnivamp specifically only heals for a fifth of its value against minions and jungle monsters — so a jungler leaning on Omnivamp to sustain through camps is getting less out of it than the tooltip implies.

Tenacity shortens crowd control, except the kinds that matter most

Tenacity reduces how long incoming crowd control lasts, as a percentage, down to a hard floor of 0.3 seconds — but it does nothing against knock-ups, stasis, suppression, near-sight, or drowsiness, which is why Cleanse and Mercury's Treads still feel unreliable against Malphite ults and Warwick ults specifically. Multiple sources of tenacity don't simply add together: items and runes in the same internal group multiply against each other, while different groups (items, summoner spells, champion abilities) stack on top of that additively, and the total caps at 100%.

Adaptive Force lets the game pick AD or AP for you

Runes and a handful of item passives grant Adaptive Force instead of a fixed stat, and the game converts it into whichever you already have more of: 0.6 bonus attack damage per point, or 1 ability power per point, decided by comparing your current bonus AD to your current AP. Only itemized and rune-granted AD or AP counts toward that comparison — stacking passives, like Veigar's, don't tip the scale, though Rabadon's Deathcap and Sterak's Gage are deliberately special-cased to count. Pick an AD champion with no AP items and Adaptive Force is a non-decision; the stat exists for the hybrid and off-meta builds where the split isn't obvious, and for keeping one rune page usable across a roster instead of swapping shards every game.

Quick reference

None of these stats fix a build that's fundamentally wrong for the matchup — a Lethality assassin still dies to a tank with enough percent penetration denied, and enough tenacity still loses to a suppression ult. What they buy is a fair fight instead of a lopsided one, which is usually all a build needs to do.