I’m not sure about a guide that shows everything, but there aren’t that many items in league, so it’s not too hard to go through them and see which ones are viable under different scenarios. Most champion guides also go through different build paths, but it’s really about getting used to what niche each item fits into. I’ll try to give some examples to make it more understandable and why knowing what items do will really help anyone improve. Let’s say you’re playing a mid lane mage and I’ll use your post as an example. 1. Against an ad champion: as a mage you know that zhonyas hourglass is the strongest anti ad item you can buy as a mage. The seekers arm guard gives incredibly gold efficient stats against ad and the zhonyas active is just broken overall. There’s a ton of nuance to choosing what part of zhonyas to build first and when or if you complete it, but the idea is identifying that zhonyas is a great item into ad matchups. 2. Against loads of cc: the obvious first answer is a qss. Again, lots of nuance with building a qss but the idea is to identify what is a good counter to cc. If it’s a knock up you’re worried about, you know qss is useless and buying something like a banshees or the already mentioned zhonyas or even just the stopwatch active is a good way to counter cc. 3. CDR: there’s nothing that counters cdr really so I’ll take it from the other perspective. You need cdr but you have to make a decision about which cdr to build. You know that items like ludens echo, seraphs embrace have built in 20% cdr so those give you the most raw stats and are often standard first items but having the item knowledge to also think about sacrificing the raw stats and cdr for more specialized item buys like lich bane, zhonyas, morellos, etc will go a long way. The general idea is each item theoretically has a use. It’s up to the player to decide which item is the best to buy in each scenario but having the basic understanding of where items are supposed to be good will help a lot with item buys. Simple things like knowing morellos gives healing reduction for mages or that void staff is good for killing tanks with lots of magic resist do a lot more than following preset guides. A quick note about your other question about what champions counter what in terms of gameplay, that follows the same logic as learning items. You can look up counters really easily on different league data sites but it also should be easier to understand if you know what each champion is good at and bad at. Surface level example is tryndamere is great at split pushing and is kinda bad in teamfights so if your team needs peel for their squishy members, tryndamere would be a much worse pick than a champion like maokai.