Kog'maw and AP Yi
Yi we were told was supposed to be an AD fighter, and his cd reset (like kat and many others) and ap ratio on alpha strike made him too op. So the ap ratio was removed, along with the cd reset on kill when highlander was active. Okay, he was op ... having the ability to do AP or AD and having ratios that allowed him to knock out huge amounts of health near instantly was wonderful if you played him, not so great if you were playing against him.
Kog'maw. Same thing only worse. He has even less vulnerability than Yi. He can hit you when you can't even see where he is, and he doesn't even have to "get close up and personal" to kill in two skill shots if he can land them.
Either apologize to all those that bought Yi when he had ap ratios and that was why they got him and return him to his prior O.P. ness, or remove the ap ratios from Kog'maw. Stop playing it both ways.