Gul'dan by Spazzo

Soulwell & Lifetap upgrade
Using a Soulwell now provides the user with an additional ability power for the duration of the restoration.
Soulwell & Lifetap upgrade
The cooldown on Soulwell is reduced by 10 seconds, and the cooldown on Lifetap by 5 seconds.
Havoc Upgrade
If one of the targets of Havoc is killed, the cooldown is halved, and half of the mana used is refunded.
Hand of Gul'dan upgrade
For each hero hit, Gul'dans basic abilities recharge 15% faster for the duration of the buff(stacks additively with similar talents)

Soulwell & Lifetap upgrade
Dying now instantly refreshes a Soulwell, and Lifetaps cooldown is refreshed upon a takedown on either team occuring near Gul'dan
Hand of Gul'dan upgrade
For each hero hit, Gul'dans basic abilities recharge 15% faster for the duration of the buff(stacks additively with similar talents)
Basic attack & Havoc upgrade
Basic attacks now leave a small damage over time effect on the target. The speed at which the damage over time applies is doubled if the basic attack was imbued with Havoc
Havoc upgrade
Havoc now deals additional damage to non-heroic targets

Hand of Gul'dan upgrade
For each hero hit, Gul'dans basic abilities recharge 15% faster for the duration of the buff(stacks additively with similar talents)
Hand of Gul'dan upgrade
Now fires three meteors rather than one, dealing 20% more total damage. The debuff is applied from the first attack, and does not stack. The meteors strike within the same period it would take for the untalented version to strike
Hand of Gul'dan upgrade
Each opponent hit reduces all basic ability cooldowns by .8 seconds, to a maximum of 8 seconds
Soulwell & Lifetap upgrade
Using a Soulwell will now grant damage resistance to the drinker. Using a Lifetap will grant a longer duration version of this resistance

Heroics

Havoc upgrade
If one of the targets of Havoc is killed, the cooldown is halved, and half of the mana used is refunded
Soulwell & Lifetap upgrade
Using a Soulwell will now grant the user Spell Shield to the drinker. Using a Lifetap will grant a longer duration version of this Shield
Basic attack upgrade
Increase basic attack speed by 10%, and basic attacks no longer have a travel time.
Hand of Gul'dan upgrade
The amount of ability power granted is increased, but the cooldown is increased by 4 seconds

Soulwell & Lifetap upgrade
Can place a second Soulwell. Using Lifetap will removes all roots, blinds and silences. Lifetap may now be used when silenced
Hand of Gul'dan upgrade
Allies within the area hit refresh their basic ability cooldowns 20% faster for the duration of the buff.
Basic attack & Havoc upgrade
Basic attacks now hit 2 targets, and Havoc now hits 4 targets.

The other Heroic
Pick the Heroic you didn't pick.
Ritual of Summoning upgrade
Can be targeted on a living player to provide them with a shield and bonus attack power, and revived players also receive the bonus attack power.
Dark Portal upgrade
Spawn another Portal with a separate usage cooldown.
Summon Infernal
Speaks for itself, ya know.

Gul'dan is designed in flavour to be the World of Warcraft Warlock, with the gameplay lending to combo usage of his Hand of Gul'dan ability and Havoc, dealing damage to multiple enemies at once.

Lifetap is designed to be a pre-fight buff or a post-fight survival, to give Gul'dan extra presence on the field, similar to how one might use a First Aid Kit.

One Heroic is inspired by the events that Gul'dan was heavily related to, whereas the other heroic is a new mechanic that is supposed to be a somewhat altered version of Abathur's Ultimate Evolution heroic, with the downside that it must be used on a deceased hero, but the upside being that the hero benefits from all talents, and it benefits from the same upsides as Ultimate Evolution otherwise, such as the enemy team not gaining anything from the takedown, aside from a small amount of experience.