Level 1-
Conjurer's Pursuit (Passive)
Hatred Knows No Bounds (Passive): Your Basic Abilities and Trait now have 25% longer range.
Wrathful Fervor(Trait): Allies who attack the target of Malice gain 10% movement speed for 2 seconds, stacking with any other movement speed buffs they may have.
Level 4-
Lightning Strikes Twice (Q): Charged Bolt now moves 15% faster, is 10% wider and pierces through the first target hit.
Avalanche (W): Freezing Skull now Slows enemies further depending on the distance it travels before hitting them, Slowing for up to 80% decaying over the duration.
Evil Eye (Trait): The target of Malice now has 12% less Ability Power for as long as Malice remains on them.
Level 7-
Limitless Hordes (E): You now have an additional charge of Call Morlu, and their health and healing is increased by 15%.
Runecharged Bolt (Q): Charged Bolt now spreads a lesser form of Malice to up to 3 targets if the primary target is affected by Malice. This form of Malice lasts for 2 seconds, costs no mana to upkeep, and allies can be healed from multiple enemies at once, with a separate timer for each. Allies who hit enemies affected by Runecharged Bolt's version of Malice are healed for 24(+4%) with a 0.55 second minimum wait between heals.
Miasmatic Bolt (Q): (Quest)
Quest: Hit heroes with Charged Bolt to increase the duration of debuffs spread by Charged Bolt by 4%, up to 100%.
Reward: Upon hitting 25 heroes, Charged Bolt gains 75 bonus damage.
Heart of Cold (W):
Quest: Hit heroes with Freezing Skull to improve its damage by 4, up to 120.
Reward: Upon hitting 30 heroes, the first enemy hit by Freezing Skull is stunned for 0.8 seconds.
Level 10-
Poison Cloud (R1)
Kiss of Mephisto (R2)
Level 13-
Malicious Intent (Trait): You can now maintain Malice on two targets for a total cost of 12 mana per second. Casting Malice when you already have two instances of it active overwrites the oldest one.
Blood Rage (Trait): Allies who repeatedly attack the target of Malice reduce the timer before they can be healed again by 0.08 seconds every time they deal damage. This reduction is reset every time they are healed.
Dark Harbinger (E): Morlus now take 45% less damage from non-Heroic sources, deal 35% more damage to non-Heroes, and increase the health of nearby Minions by 75%. They also take 15% less damage from Heroes.
Level 16-
Lightning Nova (Q): Enemies near the target(s) of Charged Bolt also take 98(+4%) damage. This damage also spreads debuffs similar to Charged Bolt itself.
Dark Grasp (E): Morlus now deal 75% of their base damage in an area around their target, and attack 20% faster. Their attacks now also have a range of 5.5.
Brain Freeze (W): Freezing Skull now lowers the Ability Power of affected targets by 20% for 2.5 seconds. Stacks with other Ability Power debuffs.
Level 20-
Corrosive Venom (R1): Enemies affected by Poison Cloud deal 6% less damage and are Slowed by 4% per stack for the duration of the poison.
Sealed With a Kiss (R2): Allies near the target of Kiss of Mephisto are healed for 18% of what the primary target is healed for, and gain 30% additional healing from Malice for 5 seconds.
The Sin War (E): The cast range of Call Morlu is increased by 250%, and the Morlu now deals 130(+4%) damage to enemies near it upon summoning and applys Malice to all affected enemies for 2 seconds. Morlus now also deal 10% more damage and move 10% faster. When the Morlu lands, it also heals all nearby allies for 40(+4%) for every enemy Hero it hits.
Iron Maiden (Trait): The target(s) of Malice now take 42(+4%) damage whenever they deal damage.
My only feedback other than that i want to give is on Charged Bolt. Not having it spread ALL types of CC/Debuffs feels inconsistent and would be akward to explain in a tooltip. Not to mention, when does the half timed portion occur? Is it based off maximum duration of the applied CC/debuff, or its current duration based on being hit by charged bolt? with how many abilties and talents there are affecting these abilities across every hero in game, it seems very odd and too inconsistent to be something you build around.
Might I suggest something similiar in my Mephisto design, where if the targeted is afflicted with debuffs, they take increased damage or something simiiar. Something still playing off the debuff caveat but still able to be consistent
The duration of spread debuffs is based on the original duration of the debuff, rather than the time left on it, this is partly to make the skill more forgiving for Mephisto and partly, like you said, for consistency. The only reason I went into such detail on which statuses the skill does and does not spread is because someone informed me that tha term "debuffs" in general was a bit too vague and asked me to clarify. Essentially, it spreads everything but Stun, Root, and Malice, which would be the ideal tooltip text.
As for the suggestion, I'd rather not give Mephisto too much conditional damage, considering how much utility he gives to a team as a whole and how he needs to more be aware of what debuffs are out on who rather than the quantity of debuffs. Thanks for the feedback, though!
edit: The rez change suggestion in the comments is also pretty neat and would make Mephisto a bit of the evil twin version of Auriel, she marks an ally while he marks the enemy.
As for the talents, since you mentioned in the parenthesis that some of them weren't quite up to the standard that the rest of the kit and tree presented. Would you mind listing some of the problem talents, so that I can change them around to make the concept as good as it could be?
How about "dooming" or "cursing" (so some sort of debuff) an enemy with a kiss which it would steal a portion of the target's health and, with that same "kiss", transfer it to one of your allies as health?
Or, to keep it lore-wise, temporarly resurrect a fainted ally to join the battle with that "kiss", in which that rezzed ally cannot be targeted by any damage until the ult effect ends (since he's dead and it's just a ghost who is dealing some dps with his own skills (ults included) before returning to Death again) (so it would be a mixed mechanic of Abathur Complete Evolution ult with Auriel's Rez and Leoric's ghost)?
That would be more demonic IMO!