Dark Harvest
Dark Harvest is a powerful rune ...when stacked.
And to stack it requires quite a bit of farming, making it a mid to late game rune as a result.
What, exactly, is it and what does it do?
Imagine if any champion could have Nasus Q built into their kit. Only thing is that you have to have been near a large minion, a monster, or an enemy champion when they die to gain a stack and to refresh the cooldown on it.
Dark Harvest stacks infinitely throughout the game much like Nasus Q and has the potential to delete any champion you set your sights on.
At its best, it is optimally used in team fights in which Dark Harvest procs on each of the enemy champions who die in it so that you can tear the next one on your list a new one.
That said, it only proves useful when stacked and, as aforementioned, requires farming.
Is this what Riot intended for this rune? A rune that promotes AFK farming for the first 15 minutes of the game before a champion can be of any use to the team?