Not really, even before they nerfed it. Its useful for when you pick a team fight oriented build. Q build is great for laning, especially when there’s just one enemy in your lane, but you lose effectiveness during team fights because in order to get value you have to single out one opponent which isn’t always ideal.
Black Harvest is more of the team fight build because your in order to finish the quest you need to mark enemy heroes for 180 seconds. You could mark one hero at a time and have it take forever if you’re laning, or you could team fight, try to mark as many heroes as possible and finish the quest much faster.
The reason I would pick it along with Black Harvest is that the extra damage only activates after 4 seconds, but your trait only lasts 4 seconds. That means if you don’t consistently AA then you won’t get much value out of it. Black Harvest increases that duration to 6 seconds (once quest complete), which gives you a bit more time to get that AA in to continue the higher damage from Memento Mori before the duration expires. Plus, this means even if you only AA a hero once, it’ll take 2 seconds of bonus damage without the need to AA again.
They’re synergistic in that regard and great when paired, however I think those 2 talents should merge into 1 because of how well they work together.
I just don’t think the damage increase is worth it. I worked out some math and found out that its not that big of a difference if you pick either Black Harvest or Memento Mori separately vs if you picked them paired.
Assuming an enemy hero’s health is 2000, 2% of that is 40. The duration is 4 seconds, so the mark deals total of 160 damage in those 4 seconds and 240 in 6 seconds. Memento Mori increases that damage by 60% after 4 seconds. If you have completed the quest and marks now last 6 seconds it will deal 40 baseline mark damage per second plus 0 bonus damage because you didn’t pick Memento Mori (or 40+40+40+40+40+40=240). With both talents paired, it will deal 40 baseline mark damage per secondd + 24 bonus damage, totaling to 64 damage per second after 4 seconds. So if you hit someone with one AA, it will last 6 seconds and do a total of 288 damage within those 6 seconds not including AA damage.(40+40+40+40+64+64=288).
Now if you were to pick Mortality instead of Memento Mori (both level 16 talents), but still picked Black Harvest this is what your damage will look like. Assuming again that the enemy hero has 2000 health, Mortality will deal 8% of that which is 160 damage per W. So if you marked someone for 6 seconds with one auto attack because of Black Harvest it will look like this 40+40+40+40+40+40+160=400.
400>288. Granted, you can extend the total damage output of Memento Mori by continuously casting AA’s and extend the mark, but the CD of W is 5 seconds, so I mean the damage you can deal with the %W trait is higher than that you’ll get with Memento Mori unless you keep an enemy marked longer than 6 seconds. Over a longer period of time Memento Mori will eventually out damage Mortality, there’s just a lot more conditions to make that happen and it won’t always happen. The other thing is that Memento Mori can deal damage team wide while W does not. So if you hit 2 enemies that total damage becomes 576, 3 heroes is 864 every 6 seconds assuming they all have 2000 health and it isn’t counting AA damage or the baseline damage from W.
That’s why its important to fit your talents with your play style, not the meta. I hope my math is correct, and if you find out its not, you’ll have done the calculations/theorycrafting yourself and seen what you think would fit you best. Personally, I pick Memento Mori due to me enjoying playing Malthael in the 4 man.