Kog's passive should make him fundamentally different from other Marksmen
I'm thinking Graves and Jhin, different here. Not, not with an ammo system. That would make no sense on Kog.
Instead, let him scale in a fashion altogether different. He's supposed to be the OnHit machine gun guy now, right? Or at least that's what Riot is pushing him as. So why not go all the way instead of half-assing it?
Passive - Eldritch Acid: Kog'Maw's basic attacks have a base AD ratio rather than a total AD ratio and deal magic damage rather than physical damage. Bonus attack damage, critical strike chance, ability power, and life-steal all modify his basic attacks with OnHit effects.
-Bonus Attack Damage grants Kog'Maw (AD ratio) flat magic damage. -Ability Power grants Kog'Maw (AP ratio) %Missing HP magic damage. -Critical Strike Chance grants Kog'Maw (Crit% ratio) %Max HP magic damage. -Lifesteal grants Kog'Maw (amount per 1%) flat healing.
I can see two mains ways to balance this. Either with higher values and Kog's W working more or less as it does right now. Or with lower values and his W scaling down to a cooldown of zero once he maxes it so that it is always available.
Generally speaking, the goal would be to make AD, Crit, and OnHit passives all equally useful on him. And just to mention now, Kog's base attack damage would still be able to crit and lifesteal normally. This new passive would make Kog arguably the worst Marksmen for destroying Towers. However, his damage against champions and monster objectives should be tuned to the high end of the scale, which is where it should be by all accounts. Thus, Kog should be picked when your team wants high selection long range single target DPS in addition to obscenely fast Baron and Dragon clears.
This Passive remake would probably require some other changes to his kit. Notably the %Armor shred on his Q would be largely redundant, though amping your team's damage is always helpful. But that's beyond the scope of this topic.


it's just the DPS item in the game.
No.
and one situational item is sorta the standard for AP Marksmen Kog.
it's non-scaling damage, but simple flat additive damage. Basically whenever an ADC buys an item this item multiplies off his other stats, say if you have IE then buy a Shiv, the shiv is mutliplying what the IE does, on the other hand, buying additional on-hit items is like adding more flat damage, it doesn't multiply anything.
, it also takes into account your base AS and adds it the same way, so you'd end up with:
and that's already 80% crit chance, so yeah, it doesn't take a HUGE number of samples to start seeing the multiplicative benefits.
His problem is that he doesn't do a lot of single target damage because his kit and (now) his items are AoE focused. When the enemy ADC is mowing down your team one by one, you've got a problem.