Read the FAQ or try searching. This has been answered dozens of times already.
You have not attached your unit to an actor. Basically actors handle all visual elements in the game and until you add your units to the events of one so it creates one with the unit to represent the unit, the unit will have no visible appearence in the game.
If you copy a unit, duplicate its actor as well and make sure it updates the event hooks to your new custom unit and not the old base unit.
Additionally you can copy an existing actor and simply change the creation etc events to link to the custom unit instead of the orignal link target unit.
Sigh.