In honour of the newest Warhammer Total War DLC, I've thought up an actual Vampire Coast
What is it? The Vampire Coast is a seemingly normal stretch of sand 8 miles long and an average of 100 meters wide. For some reason, it gained a sort of life of its own and the ability to drain life.
The coast is somewhat out of the way, and not many people walk in it, so almost nobody noticed its effect in many years. It takes 25 minutes of walking from the nearest road to get here.
Observant people (Perception DC 15) will notice that the coast lacks any life: birds are flying over it, but none is on the sand. There is no grass, no insects. Only sand and rocks. Druids and rangers always have advantage on this roll.
Inspecting the sea in front of it will reveal it lacks any sort of fish 50 meters from the coast.
Every minute spent walking in the sand, the coast drains 1HP
This is a slow and subtle effect, and hard to notice it. Victims must pass a Perception DC 20 check to notice they are losing life, and the DM shouldn't tell them it's happening. Calculate the lost HP without telling the players. Simply tell them this:
-When someone has lost 1/4th of their HP to the coast: You start feeling strangely weak and tired.
They gain 1 exhaustion.
-When someone has lost 1/2th of their HP: You feel really weak, your hands start to shake and walking is difficult.
They gain another exhaustion.
-When someone has lost 3/4th of their HP*: Your vision is blurred, breathing is difficult and your head feels light. It looks like the sand is starting to swallow you.
Another exhaustion, plus the coast starts trying to eat them.
-The coast easts: When someone has lost 75% of their HP, the coast feels their weakness and tries to eat them. A hole forms in the sand below the person feet and hands appear from it, trying to drag them down.
This effect can happen only once every hour for each character.
Hands: 5ft area of effect. The victim must make between 3 and 6 Athletics or Acrobatics check against the coast Strength check or be dragged a bit down.
The coast rolls on strength with a +5.
3 failures mean the victim is dragged down and submerged.
3 successes mean the victim escapes.
At any point, other people can help the victim. One person helping gives them advantage. Two people or helping give advantage and only 2 successes are needed to escape. Three person helping mean only 1 success is necessary. Four people win automatically.
If a person dies on the coast, the hands drag them down in 3 turns automatically.
The drain ends as soon as the victim stops touching the sand. The exhaustions go away as soon as they recover their HP.
Edit - Some clarifications
The drain works like a touch attack, so it goes through shoes, socks, armor boots and all that.
If you are riding a mount, only the mount takes damage.
If you are high enough, for example on a flying carpet or on stilts, you will not take damage.
Sleeping on the coast: when sleeping on the sand, you will wake up after losing half of your HP to the drain, feeling really sick and unwell. At this point it may be too late anyway.
Edit 2 - I just thought about this, but the players may want to try understand why they're feeling week. If they do a check (probably medicine) I suggest doing as such: If they roll 10 or less, you say "You are pale, but there are no visible wounds." If they do 10>15, you tell them "It seems you're losing energy at a rapid pace, and if it keeps happening you may be in real danger in just a few hours" and then you tell them what % of HP they have lost. If they roll above 15, you tell them exactly how many HP they have lost. If they roll above 20, you tell them "It looks similar to the effect of a spell that drains life or energy."
If they use detect magic, the whole beach has a faint necromancy aura.
How to kill it?
Hidden somewhere on the coast is a cave where its heart is hidden.
Finding the cave
The cave has a small, 5ft entrance hidden between rocks.
If the players walk along the coast looking for it, it takes 1d2 hours before they stumble into it. Fast movement can reduce the time in half, but gives 1 point of exhaustion. Walking in the sand is difficult.
In one hour, the coast drains 60 HP.
It's possible to find it by flying over the coast or sailing along it. It's much safer, but requires a Perception DC 12 to notice the entrance.
Inside the cave:
The passage is narrow but seems solid. You can feel a slight vibration through the floor
The entrance is 5ft large and tall, but it soon becomes larger. It's a solid rock cavity, 10ft large, completely dark.
This area is 50ft long.
When a living creature goes through this area, 1d6 sand-shadows spawn around them, created by the coast as a last defense, using the life force of its victims.
They use the same stat block as regular shadow, but they are made of sand instead of darkness.
At the end of the corridor is a semi-spherical, 30ft radius room with a large black heart slowly beating in the middle t. It seems connected to the rock itself.
Huge aberration, AC: 8. 10 HP + all the HP it has drained in the last 24 hours. (Keep track of them)
The heart doesn't do anything, but it has 3 lair actions. it uses 1 of them each turn with Initiative 20
Lair action: Summon 1d3 Wraiths made of sand. Can't use it again unless all wraiths are dead.
Lair action: Sand spray. A crack opens in the rock and sand explodes at high speed out of it. It hits in a 15ft cone from any point in the room and deals 3d6 damages, Dexterity 14 to reduce in half.
Lair action: Sandstorm. A large cloud of sand fills the room, obscuring vision. Everybody is blinded. It lasts 1 round. Casting spells with verbal components require a concentration check DC 14, or sand goes in your mouth.
When damaged, the heart "bleeds" sand mixed with any body the beach has eaten in the last week. Mostly this will be fishes, crabs and seagulls, but also some fisherman and whoever the players are looking for. The bodies are drained.
Why are the players there?
Maybe he's dead, and they find some of his drawings abandoned in the sand.
Maybe he's still alive, barely. He managed to climb up a rock and is hoping someone will save him.
2)A boat was forced to land on this beach during a storm. Some explorers have found the boat but it's empty, and fearing some monster was around they left. The players are tasked with learning what happened. They all died while sleeping on the beach.
3)They just happen to walk by
If it seems too difficult or too easy, change the numbers however you like, I haven't even tried to balance this. It's really just a dumb idea I've had.