Now They Fly? (50gs) - Get a kill while airborne in a Warthog. Size Is Everything (20gs) - Kill 20 enemies with a detached Machine Gun Turret. ODST (30gs) - Kill a player while you're airborne from using a Man Cannon. Bigfoot (20gs) - Kill 20 enemies using the Mantis' stomp attack. David and Goliath (40gs) - Board an enemy Mantis. Clay Pigeon (30gs) - Shoot an enemy out of the air while they use the Man Cannon. Special Delivery (30gs) - Kill an enemy with a melee attack when landing from a Man Cannon. Pump Yer Brakes (40gs) - Score the killing blow on a Mantis.