meat wagon

Anyone know how to make a Black Arrow like ability work when used by Meat Wagons? It does not seem to work for me even if I use the default ability. The Black Arrow projectile shows but not the minion (/on kill) nor the buff/debuff. (duration is long enough)

Alright so I have some ideas on changes to this unit to make it more interesting but I have no idea how to implement them. I want to make the Meat Wagon use corpses as ammunition that leave a corpse at the attack location (kind of like Disease Cloud). Now I have a few questions. How do I make...