A Quick Guide to Counterpicking

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The format will be this:
(if the enemy team has this) -> (you should consider picking this champion/item/summoner spell)

• Physical damage / auto attackers -> Rammus, Malphite, Jax, Teemo, Thornmail, Ninja Tabi, exhaust
• Stuns -> Banshees Veil, Quicksilver Sash, Mercury Treads, cleanse, Mundo, Morgana, Trundle, Olaf
• Magic damage -> Galio, Banshees Veil, Quicksilver Sash, Force of Nature, Mercury Treads
• AoE -> Janna, Gragas, more AoE champs, damage resistant champs, STUNS/SILENCES for the initiator
• Burst damage -> Poppy, Banshees Veil, Hexdrinker, high health champions, better positioning
• Healers/lifesteal -> ignite, exhaust, Executioner's Calling, Katarina, Gangplank, Miss Fortune, Tristana
• Invisibility -> Vision Wards, Oracles, TF, Nidalee
• Gankers -> Teemo, Sight Wards, global ults (SHEN, ASHE, PANTHEON, Twisted Fate, Gangplank)
• Tanky Team -> Kog'maw, Madreds Bloodrazor, Deathfire Grasp, Corki, Poppy, Xin'Zhao, Malzahar, Amumu
• Channeled spells -> any stun, silence, fear, knock up/back, or suppression
• Harass heavy-> all types of healers ( taric, sona etc )
• Glass Cannon Carry-> assassins (Kassadin, Akali, Poppy, Shaco)

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from: http://www.reddit.com/r/leagueoflegends/comments/ekpox/alright_i_havent_seen_one_of_these_around_and_id/

Hopefully this guide will help a few of you out there!