Kog'Maw's and Corki's Synergy with Items Is Terrible ATM.

There are 2 types of Marksmen right now.

There are the caster carries who build armor penetration in the early game and crit items later on. They don't buy crit early on because their abilities don't scale with crit and attack speed but they scale really damn well with AD, armor pen and cooldown reduction. Examples for this are Lucian with his Q and Ulti, Jhin with all of his abilities, MF with Q, Passive and Ulti, etc.

The other kind of marksman is the classic crit autohit marksman. They have a lot of AD, attack speed and other steroids and abilities in their kit that synergize with crit. They need some time to ramp up but once they have finished their core items they just demolish their enemies with their autos. Examples for this are Jinx with her Q and passive attack speed steroids, Twitch with his Q attack speed and Ult which gives you AOE autos and extra AD, Vayne with her Ult that gives her AD and her Q that can crit, etc.

Another mention goes to Ezreal. Because of his Q, he has a unique build all to his own that does not involve crit or the classic AD caster items and instead focuses around sheen, AD, and on-hit effects to make his Q hurt as much as possible, combined with CDR to make him able to spam his abilities.

Now, let's take a look at Corki and Kog'Maw. Both don't fit into any of the two categories above because their kits just don't scale with the standard builds of these two, at least not good enough.

First, let's look at Corki.

His currently best item that he always rushes is Trinity Force. The item itself gives a decent amount of AD and CDR, the Sheen and Phage effects are also useful. The attack speed that it gives you is kind of meh though - after all, Corki is a Caster Marksman, not an autohit-focused marksman. An even bigger problem is to decide what to build after that.

The best option currently is probably crit. This kind of sucks though, you are Corki, literally the only Synergy you have with actual critical strike and autohits is your passive - which doesn't even give you extra damage anymore after they nerfed it. You would want to get some flat AD instead of crit and cooldown reduction to make your abilities hurt more, you are a Caster Marksman.

So what do you want to do if you want your abilities to hurt more? Build what all the other Caster Marksmen are building? No, that won't work. With Trinity, a combination of items like Black Cleaver, Youmuu's or Death's Dance is guaranteed to get your CDR overcapped. You also deal 78% magic damage. Which means that 1/5 of the armor pen that Youmuu's, Black Cleaver, Duskblade and the Last Whisper Items grant you is wasted. Which also means that you have nothing to really deal with tanks.

Alright, let's get creative - AP or Hybrid? No, compared to other Hybrids like Jax and Kayle Corki's AP ratios suck. There are also only 2 Hybrid Items in the Game - Gunblade is kind of decent but Guinsoo's itself already just sucks as an item and you don't have any on-hit to profit from the phantom auto.

As you can see, every option Corki has just flat out sucks and doesn't synergize with his kit properly. In his build there is also no central scaling item like the Infinity Edge other Marksmen have at their disposal, the synergy of the items in his build with themselves and your kit just isn't there. You also won't be able to counter tanks like other marksmen do.

Next up, it's Kog.

He doesn't have any good AD scalings in his kit and all of his abilities deal magic damage, so we can already cross off every possibility of making him a caster-marksman.

So we have to make Kog a Crit Marksman. Thing is, the only thing in his kit that would make a crit build really worth is the small attack speed buff on his Q. His W on-hit, his central damaging ability, only gets better with attack speed, because it doesn't scale with AD or crit. Compare that to Vayne's Q which does scale with both AD and Crit, on top of the AD steroid on her Ult.

So what you could do, is building on-hit and attack speed items to make maximum use of his W, his main damage source. Problem with that is that Items like Trinity Force, BotRK, Wit's End etc. are made to be good on their own, they don't have a lot of synergy with each other except for the attack speed they give each other to better proc their on-hits. This is why they are so popular on melee bruisers - they only want a few damage items and build tank after. On-Hits like Kog's W and those items give you also deny you sustain because they're unaffected by lifesteal and makes dealing with tanks really hard because they can just stack resistances to counter your %HP damage and their synergy with the Last Whisper Upgrades suck. The only thing to really make full on-hit build work is to either make loads of on-hit items just for Kog ( and make Guinsoo's actually useful, I still consider Riot calling it "The Infinity Edge of On-Hit Builds" as a bad joke ) or to make what they did to the now old Kog, doubling his attack speed and by that doubling his on-hit damage output - and cause a balancing nightmare that makes you revert a rework for the first time in your game's history.

Because of that, the best option after TriForce and BotRK is Crit, which doesn't really scale with Kog's Kit as I have already talked about and makes his late game much worse than it should be.

So what needs to be done is not to buff numbers or stats or damage or anything. We just need to introduce new mechanics to the kits of Corki and Kog, that makes it able for them to fit into the two categories of marksmen. Here are two ideas I came up with.

Give Corki an Equal Amount of Magic Pen for Every Armor Pen That He Buys and the Other Way Around: Which means that if you buy Youmuu's, which gives you 20 flat armor pen, you will also get 20 flat magic pen. If you buy Sorcerer's Boots you will get both 15 magic and armor pen. Unique penetration passives like Black Cleaver will also get you magic pen.

As I already mentioned, 78% of Corki's damage is magic but he still scales really well with flat AD and CDR. This way he can get access to the classic pen caster build that Lucian and Jhin are using, without any drawbacks.

Make Kog'Maw's W Able To Crit: He can't go for a full on-hit build and he already builds semi-crit anyway, so this change would make him able to be a crit-atohit-marksman like Jinx or Ashe.

Now both of these changes would give Kog and Corki massive power boosts so adjustments should be made elswhere. But focusing on their scaling with items is just much better than trying to buff their numbers. If their kit becomes super strong on their own without items as a result of the current approach, they are missing the whole point of what a marksman should be and do.