Death passives are dumb: cause the object is NOT to die, and a good Kog player wouldn't die and thus would never use the passive then he needs a new passive.
I think that they missed a great opportunity to go more into his lore with his Passive. In his Lore Kog'Maw eats everything in sight right? He is a VORASIOUS eater, he's a glutton, he sees something and he wants to eat it. Wasn't it the second he left the Void, he just went on a crazy feeding frenzy and rampaged across Valoran like eating entire towns and stuff. The Lore never talks about him puking all the time!
Wiki quote: "Ironically, even though Kog'Maw's lore and a majority of his quotes speak of his "insatiable" hunger, every ability (except his passive) involves regurgitation."
But you never see any of that in his gameplay, all he does is throw stuff up, which is ok, but where does it all come from?
I think that his passive should be changed to one that fits his Lore:
Feed: Kog'maw eats the carcasses of dead enemies by standing over them. Each carcass grants 10 AD to 1 AA, and reduces the CD of the most recently cast ability.
Only enemies within a certain distance of Kog'maw leave carcasses upon death. Carcasses are visible to allies, and only become visible to enemies if their team has vision of him. Carcasses disappear if not picked up after 8 seconds.
And this passive idea can still be unique, Tahm and Cho both eat things, but a type of passive isn't nessecarily stepping on any other champs toes because this is a passive, not an ability and it can only be used on dead things like Thresh's passive (thresh is different enough), where as Tahm and Cho use their "eating" ablilities to damage targets that are alive.