Confused with items for an AP champion

[quote=krlxx]I am so confuse when playing with an AP champion. In theory we should be watching what items you counter buys but I get confused every time. If my counter has magic resist, then I should buy magic penetration and vice versa. What if he/she buys AP? what should I buy to counteract it? Following the logic I'd think: If he/she has 120 AP I should have 120+ AP to counteract it, if he/she has 120 MR then I should have 120+ MR and some MP, and so on with other item's qualities. That correct? Please help me. Thanks. -C[/quote]

[quote=IceCreamy]Nope, you got it all wrong. If the enemy has a lot of AP, you buy MR. If the enemy has a lot of MR, you buy MPen. If the enemy has a lot of MPen, you buy HP. The more AP you have, the more damage you deal with abilities that scale with AP (usually magic damage). The more MR someone has, the less damage they take from magic damage. If you buy MPen, you will ignore a part of their MR, thus dealing more damage to them.[/quote]

[quote=The_Nameless_Bard]this^[/quote]

[quote=krlxx]Oh that makes sense, thanks so much for you explanation. But if you tell me the more AP someone has the more damage he/she deals (buy MRes), then shouldn't it be vice versa? the more MRes someone has less damage he/she takes so I should buy AP and MPen? What about other cases? for tanks, AD, ADC and supp? How should we counteract their builds? Thanks. -C[/quote]

[quote=IceCreamy][quote=krlxx]But if you tell me the more AP someone has the more damage he/she deals (buy MRes), then shouldn't it be vice versa? the more MRes someone has less damage he/she takes so I should buy AP and MPen? [/quote] Those are 2 different things ^^ If an enemy has a lot of AP, you buy MR. If some enemies have a lot of MR, you buy MPen. If most enemies have little MR, you buy AP. It involves some maths to determine the exact breakpoint but I don't know them :P You'll generally know what you need when you're playing. EDIT: [quote=krlxx]What about other cases? for tanks, AD, ADC and supp? How should we counteract their builds?[/quote] Against tanks you buy penetration - [[Last Whisper]] or [[Void Staff]]. If they have a lot of HP, [[Blade of the Ruined King]] works. Against AD champs you buy Armor, and if they have penetration you have to go for HP. You don't have to do anything against supports, they provide aura's mostly and you can't counter those.[/quote]

[quote=krlxx]Excellent, thank you very much for you help :) -C[/quote]

[quote=krlxx]I am sorry to reopen this thread but I have another question… what do I have to understand by: magic resistance reduction and magic resistance penetration? Thanks[/quote]

[quote=Kazega]Abyssal scepter and I believe Fiddlesticks passive reduces the MR of nearby enemy's. This gets counted before any MPen is accounted for however it only works if your champion needs to be near someone for damage, see Ahri and Katarina, as opposed to champions who can strike from far away, like Karthus and Nidalee. These two concepts are not the same, though they act in a similar fashion. When you click on any enemy while having abyssal scepter sometimes you can see a negative MR, especially with a small camp like Wraiths. MR reduction helps those ADCs that do a lot of Mafic Damage like Corki and Ez as well. In short: Reduction helps the team more. Penetration helps yourself more[/quote]

[quote=DillButt64]also reduction is normally a flat amount and penetration is a %[/quote]

[quote=Kazega]J4 has a % armor reduction in his Q I think. don't think anyone has a % MR reduction though.[/quote]