okay so flat magic pen just subtracts that amount from the targets magic resitances right? That being said all ranged champs have 30 magic resistance so if a mage buys sorcer shoes and liandries assuming the ranged target has no magic resistance runes or items does that mean the mage will hit them for true damage?
Zielmann1 votesYes, they would effectively have 0 magic resist, and take full damage from your spells.
Reaper Soraka1 votesPretty much, but I think ADCs usually have like 42 MR (when they take MR runes)
It's still a very, very high amount of the damage.
Erockandroll1 votes[{quoted}](name=Reaper Soraka,realm=NA,application-id=3ErqAdtq,discussion-id=h8Fyex3d,comment-id=0001,timestamp=2016-02-03T15:44:38.639+0000)
Pretty much, but I think ADCs usually have like 42 MR (when they take MR runes)
It's still a very, very high amount of the damage.
I don't have the rune's in front of me, but is that flat, or scaling?
I usually go with scaling MR since your base MR is already pretty high. (compared to starting Armor) And more so with ADC's as magic damage would be less prevelent in the laning phase. (Unless the opponent is Corki, or a high damage poke support)
Reaper Soraka1 votesThat would be for Flat MR runes. You can still pretty much negate it if you take MPen runes (they grant an additional 14 MPen.)
TheThundersRoar1 votesPretty much.
Armor and MR can also go negative with enough penetration, which actually amplifies your damage against that target.
Zielmann3 votesActually, you can only get things negative with reduction, not penetration. 45 Magic Pen against a target with 30 MR will only get the effective MR down to 0. 45 MR Reduction would actually drop the target's MR to -15.
However, in today's game, they've made it very difficult to reduce resistances below 0. The order they take reduction/penetration into account makes it that way. It goes:
The only means of bringing a target to negative resistance is flat reduction, which is calculated first. Generally, to reduce resistances below 0, you need reduction from several sources. Very few champs (if any?) can bring somebody to negative resistance values on their own.
That brings up another critical differentiation between reduction and penetration: reduction will actually reduce the numerical resistance value of the target. If you look at their stats, you'll actually see their resistance number decrease when reduction is involved. This means that reduction is shared for any source of incoming damage of that type, not just damage coming from the person providing the reduction. So only one person needs to carry Abyssal Scepter, for example, and it'll help boost the magic damage output from the entire team.
Penetration ignores resistance, it doesn't remove it. So pen is a personal stat that is not shared with allies. It's only handled during the damage calculation, and the target's raw resistance value remains unchanged.
TheThundersRoar1 votesI see. Thanks for the correction!
TehNACHO1 votes*Reduction
Penetration has a hard cap of 0.
coeurloyal1 votesKeep in mind that champions also gain resistance per level, so their base values will also be increasing steadily throughout the game.
DeathBurst1 votesNot MR for some ranged champs, they don't.
coeurloyal1 votesCorrection: Keep in mind that most champions also gain resistance per level, so their base values will also be increasing steadily throughout the game.
DeathBurst1 votesFYI, according to the wikia page http://leagueoflegends.wikia.com/wiki/Base_champion_statistics there are 64 champions that do not get base MR/level. That's a lot.
Cave-at: a lot of them typically run Scaling MR Runes, and maybe the wikia page isn't up-to-date ("direct" pages like champions/masteries are generally updated pretty fast, but "meta" pages that synthesize information from many different places usually lagg behind).
coeurloyal1 votesRegardless of the number of champions that have or don't-have base MR per level, the point is that native MR per level is a factor that needs to be taken into consideration when trying to calculate MPen values.
I'm just trying to point out that it's a factor.
CaptnJakSparrow1 votesThe only way you can get people to negative mr is with this very specific comp
and amumu has this item 
They both also need flat pen runes + lyandris and sorc boots.
DeathBurst1 votesThe beginning of your comment looked like you had understood the difference between reduction and penetration, but apparently not, if you're talking about Pen Runes and Lyandri...
CaptnJakSparrow1 votesThe beginning of your comment looked like you had understood the difference between reduction and penetration, but apparently not, if you're talking about Pen Runes and Lyandri...
You actually do need them because there's this thing called leveling. And these other things called scaling MR runes. You're only going to achieve negative mr until about level 11-14 give or take the champion/runes/masteries. Soooo, if you don't do that very specific build the whole penetration gimmick is useless and will actually fuck you later.
-petpats- Have a downvote.
DeathBurst1 votesYeah, sure. Now go back to the top comment, the one from Zielmann, and re-read the paragraph about how Flat Reduction is applied first.
Soooo, once Fiddle+Amumu debuffs and Abyssal are applied, adding Lyandri or Pen Runes will never get you to negative MR. If enemies get to a too big enough amount of MR through leveling/scaling Runes, then you won't be able to get them to negative MR with just Fiddle/Amumu/Abyssal (too bad), but adding Lyandry or Pen Runes won't help...
