A cartographic expedition to a newly-discovered tropical island needs an escort. But surely there's nothing to really fear.
This is a stand-alone adventure intended for you to work into your campaign if you are experiencing writer's block or if your players go somewhere unexpected. Feel free change names and other details around to best suit your world. This adventure works either as a quest given to them by a higher authority (with whatever the party is currently after as a reward), or they could just stumble upon the island while traveling the high seas.
This adventure is designed for three or more level 5 characters. Creatures from the Monster Manual (abbreviated MM) are used. Many of these creatures are listed in a range of numbers. Use the largest number for groups of five or more players, the smallest number for groups of three players, and the average for groups of four.
Random Encounter
Some of the adversaries may be encountered wandering through the jungle away from their normal location. You may ignore this, throw one in should the game start to slow too much, or check with a d20 roll at the specified intervals.
Frequency Chance of Encounter
Every hour . 1-2
During a long rest 1-10
On an ODD result the party is attacked by the animated plants from hex 3.
On an EVEN result the party is discovered by the hunting party from hex 6.
The Island
The island is full of thick vegetation, lowering travel speed to half of what it would normally be (see Player's Handbook pg. 182). In addition, the cartographer Vagran wishes to spend an extra hour in each hex mapping it. Each hex of the map is 2 miles wide and has one encounter listed below, which is always found if the hex is mapped and they have not already been dealt with.
The Green Hag
A green hag named Urash has encouraged a group of wealthy human hunters from the mainland to come to the island for the opportunity to hunt halflings for sport. She disguises herself as a beautiful female elf for this purpose, and revels in the chaos it causes. Urash has paid a group of lizardmen to act as beaters, keeping the halflings in the correct area for the hunt.
The Cartographer
Vagran Giatino (male human) is the cartographer and self-proclaimed leader of the expedition. He is as proud as he is snotty, but he does have experience exploring these types of areas. Vagran is aware that he is reliant on the rest of the party should they be attacked, as he carries no serious weaponry— just a dagger, an explorer's pack and a single potion of healing.
1. Beachside
The ship has dropped anchor and sent two small rowboats containing Vagran and the party. Before they can even begin to get their bearings, a group of 6-10 native halflings (as tribal warriors MM pg. 350) burst out of the jungle. They are panicked, and if anyone can speak Halfling, quickly explain that they are being pursued by lizardfolk. A lizardfolk shaman (MM pg. 205) and 5-9 lizardfolk (MM pg. 204) are indeed in close pursuit and will soon close in on them. The lizardfolk each carry 1d10 sp.
With a bit more time, the halflings explain that they were kidnapped by the lizardmen and let loose in the southwestern portion of the island. For what purpose, they are not sure. They have always lived on good terms with the lizardmen up until now. Some feel that a curse has fallen over the island. The halflings know the island well, and could act as guides, but they mostly just want to return to their village in hex 2.
2. Halfling Village
This tribe of halflings are hunter-gatherers who live in simple huts. Their numbers total 83, most of whom are tribal warriors (MM pg. 350), with one chief (berserker MM pg. 344). About two dozen of the halflings are still missing.
3. Hut of the Hag
Urash the green hag makes her home here and has corrupted the surrounding area with fell rituals. The trees and vines are blackened, and some of the plant life has even been animated. Her small hut seems conspicuous in the middle of the jungle, but it is guarded by a shambling mound (MM pg. 270) and 0-2 vine blights (MM pg. 32).
The hut is empty, save for some dried herbs and a small mat that seems to have been used as a bed. Underneath the mat is buried a clay pot containing 70 pp.
4. Mountain
On the southern slope of the mountain in the center of the island is a stone obelisk with seven glowing gems. The halflings fear this monument. Any spellcaster who touches the obelisk can recover one expended spell slot. This drains the obelisk's power until 24 hours have passed. Anyone who touches the obelisk and does not have spell slots or who touches it after its power has been drained takes 2d6 force damage. The gems can be pried from the obelisk at risk of taking damage. Once all are removed, the obelisk ceases to function. The gems are worth 25 gp each.
5. Sinking Swamp
This portion of the jungle is especially wet and marshy. Whoever is in front of the marching order must be especially cautious and succeed on a DC 15 Wisdom (Perception) check while moving through this hex or become stuck in quicksand (see Dungeon Master's Guide pg. 110).
6. Hunting Grounds
Urash the green hag (MM pg. 177) accompanies the 5-9 hunters (scouts MM pg. 349) as they hunt the four remaining halflings in this hex. A dozen others have already been killed. The hunters each carry 1d20 gp.
7. Lizardfolk Village
This ancient stone temple surrounded by crude stone buildings is home to dozens and dozens of lizardfolk, including several shamans and their queen (MM pg. 204-5). They are hostile toward outsiders and have strength in numbers. Their temple is topped with a gold idol weighing 50 lbs. and worth 1,000 gp.