Here’s my thoughts
Heal removed
Add slow for 4% last 10sec, stacks 5 times
Teleport to enemy with Reaper’s Mark with infinite range dealing 59 damage if target is a hero deal a extra 1% of their max health
Add Reapers mark applied with this lasts 2 more seconds
Add 50% of the damage to enemy Heroes from Reaper’s Mark heals you
Changed Soul Rip slow last 2 more seconds
How broken.
Nope… he already has a 20% slow with Cold hand so… no also it no long heals
A 10 second slow wouldn’t even fly as an ult.
Oh, I see malthael killed in team fight, and then respawn(lvl20 resurrect talent) and jump right back into fight from the hearthstone 
Wont work i think
it’s 4% and pretty much stacks only if the enemy engages
You misunderstood the range of his Q
didn’t think about that
If you want to buff Malthael you have to buff him without buffs in solo lane. I dont see it happen here.
What I do like to some extent, is the idea of % sustain buff, not passive % damage buff. I actually like the idea of limiting his % damage to W. It kinda changes a lot in pretty good way.
EDIT - I would try Malthael whos all % damage comes from W (thus but to TS) or LR, while passive is limited to sustain only. + raw damage buffs obviously. % damage is kinda problematic.
theres a lot of things you didnt think about 
The only rework I believe he needs = a slight adjustment in his life steal, (soul rip heal for 4% of max health + baseline 50 or 75 or 100 health heal) ,
and , soul rip mana cost reduced from 25 to 15
tht would b more than enough
Congratulations, you just killed Malthael by utterly destroying the selfsustain he relies on.
Just for a quick comparison:
Current Q heals for 4% of enemy Heroes, on a 2s cd,
effectively you heal 2% of enemy hp per second.
Reaper’s Mark deals 1.75% per second, so your idea of 50% of that would result in healing 0.875% of their health, less than half the healing you get now.
And that’s not even taking into account the additional 25 hp/target you currently get from everything (excellent for healing on minions, summons). If this is your idea of a buff, I’m terrified of what you would consider a nerf.
Why…? 20 characters
Yea… erm… this whole “buff/rework” thread of yours lacks careful thinking and insight.
Malthael is currently the third best Bruiser with one of the healthiest talent tree according to Blizz (the dudes who have the data). So I don’t see why he should receive buffs or a rework (as bad as this one).
So you want to take away his only sustain? Good luck.
Or you can finish the quest and all marks last 2 more seconds.
I’ll keep the Q heal thanks. Minions help you stay alive too. If your healing comes just from heroes, you take away his survivability when soaking lanes and his ability to take mercenary camps efficiently.
Those changes would make him a worse solo laner. Now he only heals if he damages heroes.
Why do you want to remove the heal? its essential to his kit
My biggest gripe is that malth’s baseline waveclear and merc capture is too strong. Whilst strong pve is a good thing to have (and a big reason for his good win rate), i feel it eats too much into his power budget. It takes away from the fantasy of being a tank buster, diving around sucking people’s lives like a dementor. It doesn’t matter if you’re tough or squishy, death gets us all eventually.
When he was first released his wave clear was decent (think sonya). Now with cleave thrown in as addition damage his wave clear is nearly the best (think xul).
Id like the death fantasy to return.
Id like to see:
But in return:
Effectively, i want to shift more power towards team fights so he becomes the angel of death and away from clearing lanes so he’s no longer the angel of minions.
Malthael is still really strong against beefy frontlines. He’s a monster as long as there’s abundance of enemy healthpools nearby.