last time kog'maw was touched was patch 6.24 (LAST YEAR IN DECEMBER) which resulted in a nerf
nerf to his E ap ratio and a slight, well actually negligible, increase in W % damage.
his E, at max rank, costs 120 mana which is 4th highest mana costing ability (factoring out stacking abilities for increased mana and ridiculous ult costs). his ap ratio is at 50% and the slow hasn't been altered in ages. as marksman kog'maw this is the ability you invest in when you can't invest in QWR. it costs too much, does little damage, and slows for "4" seconds. i say "4" because it technically slows for 1 second unless you stand in it. in reality you're slowed for 1.25 seconds as you're walking out of the aoe. the worst part of this is that it has little to no interaction with his kit besides Q but Q is saved for tanks. hell, cassiopia has a similar ability that is substantially superior aside from the ap ratio. to make up for the poor ap ratio it works with her E. it roots AND slows for 28% more than kog'maw E.
W increased 1% which is a joke. lets take average tank with 3k health. from 6% to 7% you do 30 more magic damage. this is hardly anything when MR is factored.
why is kog'maw a number game to the devs? just change something to make him such a "nightmare" to balance. everyone keeps saying different things about the champ when they know little to nothing about him. how can you talk about balance if you haven't actually tried to play the champ consistently ????