Hello Ariock! Welcome to the Forums!
I hope you will enjoy your stay here!
Art of the Hero is nice one, i was always wanted to see the looks of a paladin (although it isn't a paladin
).
Life leech is a very helpful for the Korruptor, as he's mostly a tank, because his attack speed is slow. But because of it, he can't be placed ahead of the towers, neither barracks, as he is just slowing down powerful enemies, while towers shoot away. I'd like to have a second option, than the first, if it makes him more powerful.
Blood Pact is an original idea. Having an enemy who can attack, and heal the damage dealt to him is nice, it's overpowering him. It's a lot OP, considering if he can cast it on the enemy he's attacking, which means, he can hold on for a max of 6 seconds, which also gives towers even more time. However, you should add Cooldown, because without it, i can't predict if it's that powerful or not, as it would make him stun an opponent as long as his spells are ready to use. And again, it maybe connected to the Overheal.
Corruption is useless in my opinion, it's even worse, because it's already backfires you, in every way. The chance of killing an enemy unit, which is under 300 HP is not good, because it's already having low health, and it can be killed with towers very fast, which means it's useless, and also Boiling Blood already does this, and it's better. A new enemy is a bad thing too, because it would only make the towers focus fire on that lone gnoll, instead of and enemy who is stronger. Teleporting units, is even more bad, because you
don't want to them to be teleported ahead of the towers, passing through all of the defences, and losing a life or two. Healing every unit is just as bad as Teleporting, even though it does heals your units. Unless it's upgrades does get it less dangerous, and more useful, it's not worth even upgrading. Not even a single point.
Overheal. It's connected to a very two Skills above, which empowers him by a great amount. It doesn't matter how much deals damage; having a TON of hp, make him unstoppable to any boss, who can't instakill. Even anti-barracks units would have trouble dealing him damage.
Blood Hound only activates when the Overheal is in effect? If it does, than it would likely to be less useful first time Korruptor is getting healed, so it's only useful when Overheal is has reached it's maximum. Otherwise, they are a great, as they are also tanky around with that HP, However, Corruption ability makes them worse, unless Corruption is not upgraded/buffed up to some extent. Also can't say much if they don't have their stats of their own. They also would likely not last long, so increasing life span would be also good, by little amount.
Overcharge is increasing damage output for one time, and even it does, it just doesn't deal much damage, if it isn't a (true?) damage spell. And is also would likely be wasted around, as having more HP does help rather than having used all of it for a single attack, unless if there's a lot of HP can be gained, like from a Blood Seal, and of course the Overheal could be used to summon another tanky hound. However, combined with Overheal damage it may suffice to deal a lot of damage to just a single enemy.
Boiling Blood is maybe a helpful to get around with the Life Leech, as weak enemies would likely fall under it's influence, which heals him even more.
-Should his color scheme change based on the blood of the enemies in the level? Like green for spiders/zombies, blue for insects, etc...
I didn't got that part right. Do you mean, that his own armor would change the colour, as the first enemy was killed? If it is, it shouldn't, perhaps.
-I always imagined his cape as a (morbid) waterfall of blood, continuously moving/streaming, pooling on the ground beneath him
Wouldn't better having a Crimson cloak, which actually changes the colour? not the armor but the cape, which from white/silver to red/crimson/dark red, etc...
Does it seems, that your hero is having more than 5 abilities? it seems so, because only 4 are reserved for the Skills, while 1 is a Hero Spell. You have like 7.
Also, since it's fan made hero, it would be better to exist it in Fan Fiction, not Suggestions.
So, to sum it up;
-Korruptor is a natural tank which surpasses even use of the normal barracks. Having Blood Hounds and himself with HP stats so high, he can hold a chokepoint, and even discard the use of the barracks on the entire road.
-Korruptor himself can hold down the most powerful enemies with just a single use of Blood Pact, which heals him, and keeps him alive for 6 seconds, and even recharging his Overheal ability, which can be putted to good use, like Hero Spell or even summoning Hounds.
-Boiling Blood is a crowd control move, which helps against many enemies who have tend around having health mostly close to the 300 HP, as they will be surely killed in 10 seconds, if they are in the range of the effect. It's having a synergy for Life Leech, as 30 HP per kill means he would likely gain much HP from just a Swarm.
-Hero Spell, is tied with Overheal ability, which increases the next attack by 1000 and even goes higher. It may definitely kill or even cripple an enemy, who tend to have high HP, and it may be powered more, if Overheal ability takes place there.
-Unless Corruption will be buffed, or maybe at least changed, it's not worth upgrading, as it's so unreliable.
That's all i have to say.