First of all, excellent work on the HP boost. That's a good start towards balancing him.
To give him a disadvantage to balance it out he was supposed to only have limited direct damage attacks.
He actually is much more disadvantaged than that. He has poor direct damage, no kiting ability, no stun, no aoe, and no interrupt. His silence ability is different from an interrupt, as silence doesn't reset the cooldown timer (at least it doesn't for Sedna). This means opponents can teleport out without fear of interrupt. He will be weak endgame as he can't farm creeps. No stun means he won't work as well in ganks. He will remain a Tier 2 support demigod if he does not gain at least one of those things. You could give him my dual damage/heal ability, and I think he'd still possibly be underpowered.
Here is how I'd prioritize what he needs:
1. Kiting ability
4. Stun (not really necessary, but it'd be nice. )
I think in the current build these differences are to polarizing. HeadHunter is way to crappy ability and clearly isn't work putting point in at this point.
Agreed. I don't see anyone putting points into this.
But some of his defensive abilities like Holy Fury seem to be over powered.
Holy Fury does seem overpowered. There isn't an ability in this game that provides 2000 damage or healing for just 3 skill points. It's more overpowered than my suggested fix to Headhunter.
This combined with the fact that he has a low DPS in this build and no snares at all makes it extremely difficult for him to kill demigods but good when he's helping others (The same problem that the queen has.)
I would shy away from going for a support Demigod. Most people would probably use him in single player. Supporting AI teammates isn't quite as fun. Also, this game has plenty of support Demigods. Creating another support Demigod limits the matchups where your Demigod will be useable. Also, giving him flashy abilities, like invisibility and a dual purpose damage/heal ability, will increase his appeal to the players, meaning more people will try him out.
But I don't want to give him a Omni powerful attack ether cause that would feel overpowered. (And if it's duel purpose like damage and healing. That would seem like a ability you have to have) and that is something I'd like to avoid.
Every Demigod has an ability that he must get. Erebus must get batswarm, Oak must get shield, Unclean Beast must get Ooze, and Sedna must get Healing Wind II. These are their most powerful abilities, and they are not optional. I don't think that there is a problem in giving your Demigod a main ability and allowing the rest of his build to vary according to his preferences. That's how most Demigods work at the moment.
In fact, my damage/healing ability is less powerful than some abilities in the game. Take bite, for instance. It heals and damages for 775 simultaneously while reducing armor. Spit does 1650 damage over 10 seconds, and Penitence does 800 damage while interrupting, slowing, and increasing damage taken. The numbers I gave for my damage/heal ability are less than Sedna's max rank of Heal and the max rank for fireball or spine attack. You only get to heal a target or damage a target; you can't do both like with bite.
Also, it would make him a versatile Demigod. He can gank the enemy by dealing damage OR counter-gank by healing an ally that is trying to escape. Oak does precisely this with Shield and Penitence, and he's a lot of fun because he can do both at the exact same time.
Also, Assassins need to be more powerful than Generals, because Generals have monks. Making them more powerful helps them compensate. That's one of the reasons Demon Assassin, Reg, and Torchbearer have problems competing with Generalas. Unclean Beast is a Tier 1 Assassin because he's very powerful, which compensates for having no monks.
Right now I still think the mines might be a wee bit overpowered. Although I'll change how quickly the mine go off so it can interrupt something besides teleport scrolls (And the tool tip is wrong they don't silence at all but they do counter.) I feel because mines are AOE that against mana sensitive demigods like Sedna, Queen and Erebus they could quickly turn the tide of battle in a group fight. A passive ability which gives him AOE on his attacks or activates the Meta effects for his attack could be quite useful.
One minor problem I've noticed about the mines. They go off when creeps or minions walk over them. If you can micro your demigod out of the way, all you have to do is walk your minions over them. They will take no damage and will nullify your mines. If you could make them not go off when creeps or minions stepped on them, I think they would make a great addition.
As for invisibility. I think it's a good idea but it would require a skill to be removed.
If you remove headhunter, that will free up slots for you to move around abilities with. If that won't work, perhaps you could make the Divine Inspiration slot something that allows you to switch modes that unlock different abilities, such as with Ice Torchbearer and Fire Torchbearer. This would allow you to have 6 (count em, 6!) abilities for Blackulus.
I'd rather make it a passive that come into play if he hasn't moved for 6 seconds.
As a competitive Demigod player, I'm torn on this idea. I could see it setting up ganks, but that's an awfully long time to stand still. You've got to be farming creeps for xp and gold as well as capping flags. I think it'd be more useful as an active ability. There isn't a whole lot of opportunity for standing around. This will be especially problematic if your opponent has line of sight on you before you go invisible. If you have to stand to be invisible, they will probably know where you are once Angels hit the field.
On a final note, I really think Blackulus is a good idea. He looks awesome and has great potential. I'm very excited to see what he will look like. I know that some of us competitive players get bored with the same old Demigods, so if we could have another competitive Demigod to use, my clan would probably use him over vent. If he can be made Tier 1, I definitely think that we could see the pro Demigod players using him. Let me know what you think. I'm available to help test him out with any changes.