The interior of Castle Grayskull was dark, with light having barely filtered past beyond the foyer and central chamber in eons.  The Sorceress had rarely needed to descend into the bowels of the castle more often than that.  Now though, with the Slayer awakened from his eons long slumber to do violence on behalf of the people of Hyboria, she hung back in the darker reaches of the hall, the Unchained Predator all that was standing between her and the undead shambling their way...

"Rip and tear,"  She said, her voice soft but powerful as she stood behind the champion, "Until it is done."  

The zombies shambled around the corner, moaning, snarling as they locked eyes upon their quarry, and stumbled along toward the Slayer...

The slayer, Trystane Trollblood, is still lethargic and far below his potential. Clad in plate he grasped his greatsword tight before reaching for the talisman around his neck, casting Armor of Agathys and retreating a few steps as far as was possible to win a few precious moments to gather his strength.

With the spell cast and the Slayer back peddling, the Zombies were unopposed.  They continued to shamble forward with their slow gate, looking to pin the Slayer near the backmost section of the corridor.  

Trystane infuses his talisman while the zombies continue their approach. Then he moves forward 5 feet and gets closer to the wall before launching another spell at the foremost zombie.

The two Eldritch Blasts hit hard, doing significant but non-'lethal' damage to the target.  Pieces of the reanimated corpse are cast off and scattered across the ground, but it keeps shambling forward, trying to get at Trystane.  The rest follow, created a line as the move to pin Trystane into the corner.  

One, Z1, actually gets close enough to take a swipe, but it's clumsy and it stumbles, hitting nothing.  

Trystane grabs his talisman again and emits a forceful blow of spectral blades that speed towards the nearest zombie. Then, he takes firm hold of his greatsword and swipes at the same zombie. He holds his ground and prepares himself for the next zombies to engage in melee.

legendary Action: cast Sword Burst @Z1 for 5 force damage if it does not succeed in a Dex save DC 16
Action: attack with Greatsowrd @Z1, hit 21 for 9 slashing and 2 magical bludgeoning damage

The Sword Burst explodes outwards toward the zombie, but somehow it's clumsy shambling saves it from the hit.  The sword, however, is a different story, as it slashes a devastating cut, nearly severing the body in half and then knocking it to the floor, where it spilled in an unmoving heap. 

As Trystane maneuvered, positioning himself on the northern wall of the corridor, four of the zombies close in fast while the sixth shambles along, getting closer.

And then the attacks start.  The second zombie slams hard into Trystane, putting weird pressure on his leg and causing it to pop at the knee.  Suddenly the next zombie stumbles into Trystane and damages itself while the third tries to swipe a gnarled hand at him and hits nothing...

Trystane, clad in his sturdy armor, deftly absorbed part of the incoming onslaught, the metal plates deflecting some of the blows aimed at him (3 HP absorbed by Heavy Armor Master). With practiced skill, he maneuvered to parry the remaining strikes (6 HP parried), his great sword poised and ready for retaliation. Yet, the blow was so unlucky that his knee buckled under the zombie's weight and gave in. "Arrgh...," he grunted because of the pain at the uncaring zombies. 

As the second zombie collided with Trystane, his icy armor reacted swiftly, emitting a chilling aura upon impact. Frost spread from the point of contact, numbing the undead creature and slowing its movements (5 cold damage). 

As the zombies closed in, Trystane channeled the magic within his talisman once more, unleashing another brilliant Sword Burst that sliced through the air with deadly precision (5 force damage or DC 16 Dex Save). 

With a swift motion, Trystane swung his greatsword in a wide arc, aiming to cleave through the remaining undead foes. Each strike was calculated, each movement purposeful as he fought to defend himself against the relentless onslaught of the zombie horde (hit 17 for 16 damage).

The Zombies are buffeted in the onslaught.  The cold damage stops Z2 nearly in its tracks before the power of the sword burst blasts all three within its reach.  Then there's the sword itself, coming around in its deadly arc.  There's no stagger for Z3 as its body is sliced neatly in half, the two ends falling in opposite directions as it lets out one more huffed moan before its unlife ends...

As Z3 falls, Z5 steps up next to Z4.  There is a clear open path in front of Trystane for the moment, though the zombies near him continued to attack.  Z2 buffers him with a clumsy swing of its arm, followed by nasty blows from Z4 and Z5...

As three zombies closed in, their decaying fists pounding against Trystane’s heavy armor, the first two blows were absorbed by the sturdy plates, their impact muffled against the resilient metal. However, the third strike found a weak spot, slipping past the defenses and connecting with Trystane’s side. Yet, even as pain flared, the enchanted ice woven into his armor reacted, spreading a numbing chill through the attackers’ limbs. As the zombies recoiled from the frosty assault, Trystane channeled his magic once more, summoning a Sword Burst that erupted with dazzling light. Seizing the opportunity, he swung his great sword in a wide arc, the blade gleaming as it cleaved through the air, aiming to dispatch the undead assailants with swift, decisive strikes.

Three of the zombies take nasty damage from the Armor of Agathys before the Sword Burst tears through the three targets.  The zombies begin to show signs of physical damage, some more than others, before Trystane's swing of the greatsword topples on permanently.  

The last zombie closes in as all three remaining zed begin to attack again...

With the zombies in shambles, Trystane has an easy time to use his armor to absorb the few half-hearted blows that came his way. Still, he remains completely surrounded. With a quick movement, he takes hold of his amulet and stamps down his feet to send another force shockwave outwards. Then he targets the most healthy zombie with his greatsword.

Free: damage from both zombie hits is fully absorbed by the heavy armor master feat 
Legendary Action: Sword Burst Dex DC 16 or 5 force damage
Action: Greatsword at Z6, hit 16 for 12 slashing damage and 2 magical bludgeoning damage
Bonus (if a zombie staggers): Unarmed attack, hit 26! (Crit) for 10 bludgeoning damage

The shockwave sends chunks of the zombies flying before the greatsword cleaves Z6s head in half, sending the top portion of it spinning across the floor.  A puff of dust fills the air between Trystane and Z6 before it collapses.  Z2 and Z3 continue to attack, but only Z3 has any chance of doing damage...

Trystane defends the blow of one zombie but he quickly realizes that he will be too slow to also block the attack of the second one. He turns his padded shoulder piece to absorb the incoming blow but it is even too strong for that and takes a little bit of wind out of him. In a fluid move he grasps briefly his talisman and conjures a new Sword Burst, before grabbing his greatsword with both hands and bring all his weight behind a blow that should prove devastating for one zombie.

Free: three points of damage from zombie 3 are absorbed by the heavy armor master feat, one damage taken
Con save against blinded, DC 10, 7
Legendary Action: Sword Burst Dex DC 16 or 1 force damage
Action: Greatsword at Z6, hit 13 for 14 slashing damage and 2 magical bludgeoning damage
Bonus (if a zombie staggers): Unarmed attack,9  hit for 5 bludgeoning damage

Both zombies get nailed by the explosion of force, and then Z6 is annihilated by the swing of the sword.  The last zombie is barely hanging on as it reaches out and rakes claws uselessly across the Slayers armor, and that's when he reaches out, his thumb hooking into the zombie's eyesocket as his hand grips its head and squeezes.  The creature's undead skull fractures and breaks, rotten brain matter rolling out between the Slayer's fingers as the zombie topples.  

"I think that's all that is inside."  The Sorceress says, rushing up next to Trystane.  "Here.  Let me sooth your wounds."  

She holds her hands out, blue energy washing through the DOOM Slayer's body as his aches and ailments are washed away.  He feels stronger following the fight, like the dust is getting knocked off those old skills.  

"There are more outside.  I'm afraid there are more baring down on Castle Grayskull.  You'll have to clear the way if you're going to get out of here alive.  Once you're gone, I'll seal the doors best I can.  I imagine they'll be too focused on you to worry about Grayskull anyway.  You're what they're after.  What they seek to destroy."  

She leads him through the halls and out the gate of the fortress.  Outside, light snow swirls over the sands of the Shem Desert, where the castle stands.  There are two more zombies shambling up the stairs, with a skeletal soldier rushing up ahead of them, his body clad in armor, a sword in his hand...

„Thanks for the help,“ responds Trystane when he follows the sorceress. „But where should I go to root them out? To silence them once and for all?“ Trystane feels refreshed and the combat with the zombie was invigorating. His senses are already much sharper and he even feels some of his arcane prowess seeping back. While they walk together he recharges an essence rune that had appeared on his forehead. He knows that there should be many more but he will need more time to reach his full power. Time that the encroaching undead wish to deny him.

Once the skeleton starts shambling towards him, he aims two beams of Eldritch might at them and lets the undead approach.

"Follow the ceaseless advance of the horde."  The Sorceress says, adding nothing specific for an answer.  "I believe they will lead you toward Nockmaar, to the southwest, though I don't know where to from there.  You will be able to hear my voice, however, no matter where you are.  I will guide you from Grayskull."  

She watches as he moves toward, firing his Eldritch Blast at the skeleton, and watching as it breaks harmlessly over its armor.  The skeleton barrels forward, making a beeline for Trystane, while the zombies shamble slowly behind...

„Nockmaar? I’m still not able to recall my memory’s, never heard of that place as far as I can tell. But South sounds good, never much cared for the snows.” Trystane replies calmly.

With the skeleton storming towards him, he releases another blast. He retreats 30 feet southeast and there he traces arcane symbols into the air to conjures a protective barrier against the undead. Then he takes his greatsword into both hands in preparation for the pursuing skeleton’s attack.

Legendary action: Eldritch Blast @Z3, hit 9 (crit fail)
Action: cast Protection from Evil and Good

Nockmaar will be west by southwest.  Once you've dispatched the forces around Castle Grayskull, follow the trade road through the Shem Desert.  I will guide you.  

The voice of the Sorceress echoes in Trystane's head even as the fight breaks out.  The Slayer moves, his Eldritch Blast sloppy and sailing past the skeleton with no effect.  The Skeleton stumbles along after him, swinging its sword but hitting nothing...

The zombies and the skeleton continue their advance on the Slayer...

Trystane likes to believe that his arcane barrier deflected the skeleton's strike and when it did miss he was ready for an attack of his own. Then, in preparation for the advancing zombies, he paints another arcane symbol that will shore up his defences even further.