Manticore Venom and Clash of Kings
Does killing a unit with Oberyn's manticore venom implies additional point from killing a unit with your commander as per Clash of Kings' rule?
NO
NO, for Clash of Kings rules it has to be killed with an ability or attack, and abilities are listed on unit cards or attachments. Manticore's Venom attached card isn't an ability of Oberyn by itself, cause Oberyn's ability is to attach the Manticore Venom card.