I really enjoy spells which reward microing your hero, and this provided that in plenty.
- Sometimes if you are in very close melee with the target (you need to walk right up to them, closer than melee attack range) the spear misses them.
- On effect you could add an item orb ability that changes missile art to nothing, so you don't sometimes get a double spear throw. Then remove it on attacks where no effect occurs.
You might even be able to use damage detection using this method and changing the missile art to the longinus spear, then only create the projectile on damage, which would look and work a lot better than the current method.
- Because the ability costs mana, wouldn't it make sense for it to be toggleable on & off?
You could make it an arrow ability, or, if you want to leave it as a passive, do something similar to immolation.
- onDestroy should be private