The first spirit is released after three seconds, and the rest are 3 seconds apart.
As soon as a spirit appears it targets a random minion and flies towards it.
The spirit cannot target minions inside of Black Hole.
The spirits can target invisible minions.
The minion gains 100 health after the spirit reaches it.
If the targeted minion dies while the spirit is in flight then the spirit flies to where that minion died but has no effect when it gets there.
If a minion enters Black Hole after being targeted by a spirit, the spirit still flies towards it. If the spirit hits while the unit is inside of Black Hole then it has no effect.