The motives to get your party to enter the dungeon are set. Now it’s time to select the encounters. The number of these in a session will ultimately determine the length of the adventure. I consider four hours of gameplay to be everyone’s maximum attention span. In that time period, I strive for no more than two initiative-rolled fights—the mini boss and boss.
Gameplay usually starts slow as players put away their phones and get into character. Any fight that takes place in your first hour should not require initiative. Instead, make the encounter a trap or roleplaying opportunity. Define the danger early on so players know what's at stake while getting to experiment with the game mechanics.
If the players are heading to an oasis temple, have a mummy explode from the sand and deliver his Mummy Rot to a member of the group. The mechanics of the debuff can be dealt with later. For now, tell the player their skin feels rough and itchy. Over the next few hours of their in-game journey, explain how the tips of their toes and fingers have begun flaking away, slowly dissolving into sand. If you know the party has a Remove Curse spell, let them flounder until they figure it out. For now, insist only that they reach the healing powers of the oasis temple.
Next, have the player explore the outside of the dungeon. Let them see what kind of traffic, if any, moves in and out. If it’s full of goblins, make an event out of killing those outside before they can alert those inside.
The first true encounter should show up about an hour and a half into play. They can be imposing combat challenges or an early encounter with the final boss, perhaps in his lesser form. Use this encounter to teach the players about an important mechanic for the final boss. Take advantage of new player spells or items recently acquired. Be patient and allow them to stumble through and figure out the mechanics without serious consequence. Only during the final fight should you penalize them. A ward that stuns the mini boss causes the boss to target someone else.
Let them eat up spell slots, item charges and healing spells before your final encounter. If your players intend to rest, let them know the difficulty of doing so. The villain might escape or nightfall might bring more powerful creatures up from the Underdark.
Undead make leading into a dungeon easy. The presence of undead naturally suggests a higher profane power at work. Townsfolk are understandably afraid and eager to find help. The horrible abominations coming from the lair showcase the final villain’s depravity and intelligence. Widely understood tropes, like zombie moans and graves, easily build an atmosphere for players.
The small town of New Vigil lies between two great cities, serving as a minor waystation for travelers. Everyone in town either works at the local inn and tavern or tends to the church and its graveyard. Recently, the town has been beset by wandering undead coming out of the hills to the east. Skeletons and rotten corpses shamble from up the road, attacking trade caravans and slowly following travelers to the town walls. New Vigil has broken its long solitude by calling for adventurers to clear whatever foul magic is raising the dead up the road.
After arriving, the adventurers encounter few villagers out and about. Fear has gripped the town and most have locked themselves away. The limited cast of characters in town can help guide the players to their destination. Once oriented, they set out along the east road in search of the lair.
After walking for an hour, they come across an abandoned trade cart. There are no bodies, no horses and the goods from inside are missing. Perception checks receive signs of a struggle with deep nail marks running along the box seat and damage from a considerable slam to its side.
As they continue, one of them (preferably the most skittish of the group), spots a hunched being spying on them from a junction ahead (passed to them with a note). As they approach, it lopes up the north road. Tracks suggest the road has been recently trafficked by bare feet, and the adventurers head into the hills as dusk begins to settle.
While making their way up the path, the perceptive player continues to catch glimpses of a hunched, six-eyed figure watching from the darkness. As they draw close to their destination, it jumps out, wrestling the player watching it to the ground, causing the first non-initiated encounter. Its unearthly strength causes difficulty as it chokes its victim and throws off players who attempt to remove it. If left to its own devices, it runs off with the unconscious player. Most likely, the creature is put down by the eager party members. Any fire attacks immediately and violently burst the creature into flames. Upon inspection under torchlight, the players find a dirt encrusted workman whose face is caked in black sludge. Embedded into the sticky goo are six eyes, three different sets.
At the end of the trail, they find an old, condemned silver mine and a small, abandoned guard camp. Successful Knowledge (History) checks inform the players a mine shaft collapsed on 11 workers. It was since closed.
As night descends around them, they are beset by their first initiative encounter. Rolling up the road behind them propelled by 20 sets of hands, a ball of overall-clad bodies held together by thick, black goo at its center cart-wheels its way toward them. 10 broken mouths let loose a scream. The abomination charges, attempting to run them over and maul those it passes by. Fire once again succeeds in causing dramatic damage, though until fully put down, this only creates a rolling inferno ball of undead. Once defeated, the players continue their quest into the mines.
The players have ample chances to stock up on the surrounding abandoned supplies of lamps, oil, torches and mining picks. Along the way, you can reward them with raw silver for Strength checks and other puzzles that open side shafts. One such shaft unveils the former resting place of the doomed miners and their harrowing final hours. The chamber is laden with dark magics and two empty barrels lined with tough, dried, black sludge sit open and empty. Eventually, they reach a roughly hewn tunnel cutting a circular tube through the hills heading west.
The hour long journey takes them downhill, eventually ending in a cavernous workshop. Slabs of stone sit with empty coffins scattered among them, covered in thick, rich dirt. In the corner, a massive embossed vat churns boiling black sludge inside with nearby barrels waiting to be filled. The room beyond rings with the sound of pickaxes on stone and the slop of wet earth.
Inside, the necromancer rides his recently acquired risen horse, arms grafted with black goo to its equine sides which swing pick axes to extend the chamber. Undead work, digging at the ceiling, and as the players watch, a great wave of dirt lets loose, carrying with it a coffin. The necromancer dismounts is steed and with a quick spell and application of black sludge, the body rises and joins the others in their work.
Should the players light the barrels, the dome explodes, revealing the church alongside New Vigil, showering the surrounding area with grave soil. The necromancer, his horse and the risen workers fight to the death. The quest is complete, but questions as to the origin of the sludge remain a mystery, prompting further adventures.