[{quoted}](name=My Waifu Chocola,realm=NA,application-id=3ErqAdtq,discussion-id=RkX8YQU6,comment-id=00030000,timestamp=2016-10-24T17:03:06.421+0000)
Wouldn't reworking E be the better choice compared to Q if you want him to shred resists? His Q already does that and E is MOST OF THE TIME the harder to balance spell out of his kit since if it is remotely strong compared to Q or W he can max it first and farm waves with it to negate his "weaker" early game (also enables AP Kog to an extent).
Passive - Eldritch Acid: Kog'Maw's skills and basic attacks apply stacks of Acid to enemy units hit, shredding (flat number Y) resistance per stack for four seconds.
Q - Caustic Spittle: (passive IAS removed, cooldown decreased dramatically and damage adjusted) Kog'Maw fires a corrosive projectile that stops at the first enemy champion hit, dealing damage and applying the Corroded debuff for 4 seconds. Corroded converts Acid stacks from flat shred to (percentile value, multiplicative) with a minimum of Y per stack. Consecutive applications of Caustic Spittle increase the power of the percentile shred and refreshes the duration.
Something like that. It's the best way I can think of to include both flat and percentile resist shred in the same kit without them interfering with each other.