Try this,
Attack - Maximum Number of Targets = 1
Attack - Weapon Type" = Missile (Bounce)
Attack - Half damage radius = 400.00
(if still don't work, try to copy all fields related to "Attack - 1", from huntress unit to your hero)
Then,
Make a spell "Moon Glaive" with 3 levels that as you know it doesn't gives any effect.
Make upgrade , copy from moon glaive upgrade, make 3 levels same with levels of Moon Glaive ability. Apply this upgrade to your hero.
Finally,
if your hero learned this skill, make a trigger so it increases the level of moon glaive upgrade for this hero.