Mannoroth the Destructor by MarioToast

Level 1:

Total Annihilation: Repeatable Quest: Killing enemies with Execute increases its damage by 1. Heroes increase it by 10.
March of the Legion: Cleaving Charge moves 40% faster.
Quest: Trample enemy Heroes with Cleaving Charge.
Reward: After trampling 5 Heroes the slow lasts for 1 additional second.
Reward: After trampling 15 Heroes Mannoroth leave a trail of fire when he moves for 4 seconds, dealing 40 damage per second to enemies.
Deep Breath: Howl of Terror has 30% increased radius.

Level 4:

Impaling Charge: Increases the range of Cleaving Charge by 30%. Instead of swinging his weapon, Mannoroth holds his weapon in front of him, dealing 120 damage to the first enemy Hero hit and pushing them along with him.
Violent Thrashing: Cleaving Charge deals 50% increased damage but also deals damage to Mannoroth equal to 5% of his maximum Health. This can trigger Blood of Mannoroth.
Blood Barrier: When Blood of Mannoroth activates gain 15 Armor for 3 seconds.
Amplified Healing: Increases regeneration effects and all healing received by 30%.

Level 7:

No Escape!: Mannoroth gains 15% increased movement speed when moving towards enemies he has recently damaged.
Siphoning Blade: Basic Attacks, Cleaving Charge and Annihilating Strike heals Mannoroth for 15% of the damage dealt.
Poisoned Blood: Blood of Mannoroth poisons enemies, dealing 90 damage over 3 seconds.
Demonic Momentum: Basic Attacks reduce your Basic Ability cooldowns by 1 seconds.

Level 10:

Doom
Rain of Fire

Level 13:

Massacre: After killing an enemy, Mannoroth gains 5% increased Movement and Attack Speed, and 2.5% increased damage for 10 seconds. Stacks up to 10 times.
Piercing Blows: Execute and Basic Attacks ignores Armor.
Shattering Shout: Howl of Terror reduces Armor by 15 for 3 seconds, and deals 200 damage to Shields.
Desperation: While Mannoroth is below 30% maximum Health, his Basic Attacks deal 20% increased damage and restores an additional 30% of the damage dealt as Health.

Level 16:

Blood-Rage: Whenever Blood of Mannoroth activates, Mannoroth gains 20% increased damage and Movement Speed decaying over 2 seconds.
Devilish Echo: 4 seconds after casting Howl of Terror, cast an untalented version of it.
Unbreakable Charge: During Cleaving Charge and for 2 seconds after Mannoroth is Unstoppable and gains 25 Armor.
Charge of the Legion (requires the final reward from March of the Legion): During Cleaving Charge and for 2 seconds after Mannoroth leaves behind Felfire, which lasts for 6 seconds, deals 60 damage per second and slows enemies by 33%.

Level 20:

Doom For Everyone!: Doom deals 50% less damage but affects ALL enemy Heroes globally.
Hellfire: During Rain of Fire Mannoroth is Unstoppable and deals 60 damage per second to nearby enemies.
Hemorrhage: Reduce the cooldown of Blood of Mannoroth by 2 seconds. Additional applications on allied Heroes refresh the duration and stacks up to 4 times.
Demonic Resurrection: Upon taking fatal damage, Mannoroth is resurrected with full health at the location he died after 2 seconds. Upon resurrecting, he unleashes Fel Flames that deal 300 damage over 4 seconds to nearby enemies. Killing a minion reduces the cooldown of this ability by 0.5 seconds, Mercenaries reduce it by 2 seconds and Takedowns reduce the cooldown by 10 seconds. Cooldown: 300 seconds

Selected:

Witness the power of the Legion!

Battle Starting:

A new battle, a new team of enemies to slaughter.
This world will be unmade...the lives of its inhabitants undone as nothing!
Are you ready for the massacre we will unleash?

Battle Starting Response:

Ah, I can't wait...
Agreed.

Battle Starting With Someone He Doesn't Like:

What? How am I supposed to work together with such a pitiful creature?!

Battle Starting With Someone He Doesn't Like Response:

Silence! Or this alliance will end with your head on a pike!

Battle Starting With Thrall:

Ah, Thrall! Tell me...how's Grom these days? *dark chuckle*

Battle Starting With Garrosh:

We finally meet, Son of Hellscream...odd...it feels like I've already met you before...

Battle Starting With Gul'dan:

You've summoned me for this petty battle, Gul'dan? This had better not disappoint me...

Battle Starting With Any Orc:

Your blood is mine! As is your whole misbegotten race!

Battle Starting With Butcher:

I like your style. Would you be interested in joining the Burning Legion?

Movement:

Yes...
To the slaughter!
I'm getting impatient...
We will burn this world!
Don't waste my time...
What a foolish ploy!
On my way.
The end comes.

Attacking:

Tremble before me!
*roar*
*evil laughter*
This will please me.
I think a certain finesse is called for here. RAAAARGH!
Oh, my pleasure.
Finally!
Time to slaughter!
Fear the Legion's might!
The Legion will find you... No matter where you flee...

Poked:

What?
I think I stepped on an ant...AWESOME!
I'm a 8000 pound bloodthirsty demon the size of a bus, armed with a giant two-bladed spear. Is poking me really a very good idea?
Unh, I think I have someone stuck in my teeth.
Has everybody gotten doom? If you haven't speak up! There's enough doom for everyone!
Magtheridon kept telling me I always lose my head. Heh...looks who's talking now...
For the last time, no. I've never had a beard! Any evidence to the contrary will be cleaved in half!
...look, I was in a weird phase. Brutallus told me it looked good! *sigh* Never take fashion advice from a guy with blades for hands!

Kill:

*loud evil laughter*
A worth effort...but futile.
Squirm! SCREAM! *laughs*
Fall to your knees!
Die, mongrel.
I am the destructor!
Yes...this is what I came for!
Fall and die before me!
A deserved death.
Useless.

Killing An Orc:

Your blood is mine. I'm only taking back what belongs to me.

Killing Garrosh:

This was the son of Grom Hellscream? Pathetic.

Killing Murky, Brightwing, Li Li:

You'll be a fine snack.
Oh, sorry. Didn't see you down there! *laughs*

Killing A Diablo Demon:

And you call yourself a demon? Pathetic.
The Burning Hells will be absorbed into the Burning Legion.

Kill After Death:

Even death can't stop my rampage.

Ally Gets A Kill:

Hm. Not bad.
Hey I wanted that one!
Are you sure you're not a Pit Lord in disguise?

Entire Team Is Dead:

When we return...they will know our true power! And they will suffer...

Killed:

NO! I'M SUPPOSED TO KILL YOU! I'm...agh...
This cannot be...
I will not be torn from this pitiful world! No... NOOOOOOOO!!
*roar*

Killed By Murky:

Is this...some SORT OF JOKE?!

Respawn:

I return from the darkness of the pit.
You let me die one more time, and I'll come for you next!
I've lost count of how many times I've returned from death now...
I will always return.
There's still more to kill...
I will not fall again.

Blood of Mannoroth Triggers:

Drink up!
Let the Blood Curse empower you!
*evil chuckle*
Come and have a taste!

Casting Doom:

Doom for you!
That tingling you feel? DOOM!
I cast Doom as I please!
Your torment increases the power of Doom!

The Enemy Survives Doom:

Doom...does not fail!

Doomguard Summoned:

I dare summon you!
Welcome to this world...now kill!
*evil laugh*

Casting Rain of Fire:

BURN!
I will incinerate your flesh!
Run, cowards...run from the flames!

Resurrecting:

You will never stop me!
*evil laughter*
I have returned!
I...AM...UNSTOPPABLE!

Healed:

You...are worth thanking.
I bleed, you heal. Do this and I will keep you alive.