Tell me what you think! Very first time DMing for my friends and I had some fun dreaming up my very first BBEG.

                   As you ride atop Irl, the last of the black dragon brood, and overlook the village that is soon to be your next victim, your icy blue eyes drift to your gauntlet. The ring you wear, burnished from eons and still on your finger, summons a single tear that turns to ice as it falls from your gaunt cheek. It had been a millennia since you last cried, since you last felt... anything. Perhaps it was from a memory harbored by your soul long entombed within your corrupted body. The memory of Helena. It takes you back to that day so long ago.

                 Helena was yours, the most beautiful woman you had ever witnessed. So pure and full of light that her love caused you to forsake even your oath as a paladin to the Brotherhood of Liodyetie. Rare was it such a mortal being could rival the goddess of youth and beauty, yet for a time she was yours. Stolen by your king who seized her from your arms for his own. Lord Cornwell, a pudgy and greedy man took her from your hearth in the dead of night, the sound of Helena calling for you had plagued your mind every night as the last words you heard from her. You had used your name to collect a formidable army to lay siege to Castle Cornwell, the tower where he had locked her away. You had stormed ahead of your men, emboldened by her embrace once more. As you scaled the tower, hope and light filled your heart to see her beauty again, only to drain to sorrow as you burst through the tower door. Cornwell, that wretched ****, stood over your bride. Bloody dagger still in hand, he turned to you and shouted "Filth such as you are undeserving of the love of such a woman. She was fit for a King! But if I cannot have her, NO ONE CAN!" A few simple strides and a single swipe of your blade was all it took to release that worm of his head. You had cut through swaths of his guards, far better fighters than what this swine lard could have ever been. Corwell was not match for you. His head made a wet slap on the floor as it tumbled away and his body dropped. But you paid it no mind. You looked down upon your beloved, robbed of her beauty, of her life, and scream out to your god in unanswered pain. 

                  "This reminds me of the day we first kissed, do you remember?" your meek smile hardly hiding the sorrow in your voice as you hold your beloved in your arms. Her body already turning cold. "The snow was falling then too." you say as you brush the fleck of ash from her blue cheeks. Despite the clamor of war below, despite the fires and the raging battle, to you it is just you and Helena at the top of the crumbling tower. Her azure gown now stained with blood

                   "I can make you whole again. I can give you the power to bring her back as she is to your arms." a whisper comes from the shadows. Like a dark mist, an apparition glides to your side. "Serve me and I will allow you and your love to live together... forever." its voice harsh and unworldly. It would send chills down your spine if you were not already devoid of emotion. "what are you spirit?" you ask, your voice seemingly miles away from your body. "Hahaha" a cold laughter responds. "I am no spirit. I am Uel, very much of flesh and bone as you. I greet you in this form to show you my mastery of death... and life" it rattles. "Join me and this power may be yours as well. Such a power to revive this poor beauty. Such a power to make her yours again."

                    "I am Karz, Paladin of Liodyetie. I swore an oath to the pure goddess to live a life of justice, kindness, and light. To forsake that oath is to forsake my life." you respond.       "You fool" the shadow hisses. "You are already forsaken by your goddess. Where was Liodyetie when your home was ransacked? Where was Liodyetie when your love screamed your name as she was ravished by this man? Do you feel her light now, as you hold the corpse of your bride?" Its words hurt, if only for the truth they hold. Ever since you began this quest, you had not felt the warmth of the goddess of light within you. Ever since you first raised your sword, you have not felt peace. "It is true" you say in a sob. "No goddess of love would allow such a cruel fate to my Helena..."

                   "Then join me, paladin. Shed your bindings and join me and I will give her back to you. Act quickly before her soul goes to the Beyond where you will never see her in this life again." it says, an obscure hand reaching out. "Fine, creature, if the light does not bring me my love; then perhaps the darkness will. I accept your Devil's Bargain" you lower Helena and turn to the shadow. "I am yours, Uel. Give me the power to bring her back." at these words the shadow rushes you. you feel a tightness around your throat as the shade solidifies into a shackle around your neck. you hear a cackling laughter, this time not from the room but from within your head. "Turn then, my knight, and look upon her beauty once more."

                 There is a shuffling and groaning behind you as you slowly turn around. Helena stands before you, azure gown flowing in the wind just as the blood falls from her neck. Her glossy eyes reflect the moonlight as her head lollops to the side. "Behold your Helena, brought back to you as she is!" the voice in your mind cackles."WHAT HAVE YOU DONE!" you bellow to the dark room. "This is not Helena! You revived an abomination!"

                "I have revived nothing, Lord Karz. For you are the Death Knight. It was your weakness that led you here. Now claim your prize quickly, I have much use for you after." You walk to your bride, " I am so sorry, Helena. I am so sorry for being this weak. Please, forgive me." She makes a gurgling groan as you use your last remaining free will to end her undeath and lay her to rest once more. "Such a pity you did not like my gift, Karz. However, your bond has been made. Come to me now, we have much to do." Against your will your body moves you. Out from the tower, out from the kingdom, and into the darkness.

I think the story and drive you BBEG is great, even I was anger Helena was taken not going to lie, I would have do the same thing as Karz except with more anger). But I am wondering will the player get to meet abomination Helena during their travel and use her against Kraz? I dont know, I never DM before and/or dont want to get in the way of a DM's story. Also I was a bit confused is Kraz the Big Bad Evil guy or is it the darkness. all and all amazing job

I had gone a bit wild because I really love worldbuilding and lorecraft. I apologize if my explanation gets a little disconnected.

First, Karz is now a lieutenant (or slave i guess...) of Uel, a warlock who is stuck in the godrelm now fused with a Great Old God, Ho 'og (lovecraftian space squid monster). There's a myth in my world, long before the campaign takes place, when Uel attempted a massive spell to enslave this god. Heroes stopped the spell in time and instead the tentacles of Ho 'og latched onto Uel and sucked him into a different reality. However, Uel is now so powerful he can influence this world and is gathering an army to summon him back.

Karz is the first villain the party will deal with through levels 1-5ish. And as luck would have it, our cleric's backstory is that he has a jar of dirt given to him by his order with a grand mission to find some zombie (who is now Karz lol). This is completely independent of me, the player knows absolutely nothing of my story yet, it's actually sort of played off in his backstory as his order's excuse to get rid of him (because he is really really dumb with an Int of 6 i think.) After I found that out, he is now carrying a jar of Helena's gravedirt, which I will disclose to the party whenever we do a session that highlights the cleric. If he does something imaginative, or at least connects the dots and uses it against Karz; They will find out this little backstory. But sadly, Karz will have to be sacrificed to bring Uel back to our world. Uel really is a dick, but Karz has done some horrible things in Uel's name as well.  :(

And just for me probably, the very first paragraph happens quite literally in the first session. The party is at a festival in a port city called Donegras where they celebrate the myth above and show off a magic mcguffin related to it. Karz then attacks the city, steals the magic mcguffin for Uel's spell, and kidnaps a bunch of villagers for sacrifice to charge the mcguffin. 

Alright fine, since I can't stop now and because all this story is killing me to keep to myself.

The players spend their first part of their session with an NPC named Gregory and taking him to Donegras (try and get them attached to the npc and all), he cant shut up about his love and hopefully bride to be who lives in Donegras named Leona. Well, she gets kidnapped by Karz with the other villagers, Gregory helps the party chase Karz through the nearby woods to a castle tower (first big dungeon of the campaign).  They are too late as Leona is sacrificed to charge the mcguffin. Enraged, Gregory runs ahead while the party is slowed by a combat with zombies and skeletons. When the party finally catches up, they see Gregory slain by Karz who then resurrects the lovers into a banshee and wraith for a boss fight before he flys away on his dragon. Just to highlight how far he is gone that he does the same to others that happened to him. I hope I can get the players really into the story, and everything works out this way. I feel its a pretty solid nut punch and something memorable altogether. But I fear it may be too dark lol.

Holy, what a story. I give you props for your world building skills, my goodness. I think the story is great and immersive, but its not my decision how immersed your players are/want to be. Also I don't think its really that dark to me anyway (I read and write a lot of dark back stories that I kind of got used to violence's and traumatic stories), but in my opinion it also depends on the experience of your players as well.(take my opinions with a grain of salt as I am not pro or even good at DnD, I haven't even been in a session yet so keep that in mind, I am sure veterans might have better advice than me) If there inexperience in D&D lore and stories and darkness in general, they might have a hard time stomaching a story like this. All that being said, you will be fine and I hope your players get as invested in the story as I am.(Also I don't think you should be posting the future events of your story on Forums just in case one of your players see it, I suggest sending a private/direct message to someone you want to share your story with.)