Fiendish Forces | 5e Adventure Ideas

October 07, 2023
Posted by Luke Hart

By Owen Davies

Do you sometimes find it challenging to think up the next big adventure for your 5e campaign? Let us help with these five free 5e adventure ideas!

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Fiendish Forces

The adventure ideas below have been built from the ideas of those of a fiendish nature, the devils and demons of the planes. You can use what is written to flesh out adventures for your game, altering and customizing elements to fit the playstyle of you and your players. Each idea is split into suggested tiers, which indicate the levels for which such an adventure is recommended.

Local Heroes (Levels 1-4)

Fires and Fanatics

Creatures. This adventure features the following creatures: bearded devil, cultist, cult fanatic, imp.

Premise. The Emblazoned Sky is a small cult of religious fanatics who believed that the fiendish beings that lived in the realms beyond must help to restart the realm by killing those who inhabit it. The Emblazoned Sky’s leader, Aern Ly’kron, made a deal with a bearded devil to gain some magical abilities and impish creatures that would allow for the progression of the cult’s goals. The cultists and their new fiendish allies have been terrorizing the people in several local villages, stealing resources and valuables.

Plot Hook. The council of a local town has put up a job posting for a group of adventurers to look into the actions of The Emblazoned Sky and how they have garnered so much power so fast.

A Town Rift

Creatures. This adventure features the following creatures: dretch, incubus.

Premise. Cryndas is an incubus posing as a local noble within the town. Recently they have been tasked with causing some chaos using a rift that was opened in a magical experiment gone wrong. This has allowed several dretch to enter the material realm and a slow invasion to begin. Several townsfolk, influenced by Cryndas, have gone missing to feed the dretch.

Plot Hook. The local militia has sent out a notice for a group of adventurers. Also, a local mage is spreading rumors of a rift to another plane and is looking for some people to fix the rift that will infect the local area with strange creatures.

Heroes of the Realm (Levels 5-10)

A Summoner’s Foley

Creatures. This adventure features the following creatures: cult fanatic, glabrezu, mage, quasit.

Premise. The mage Uldrasir Highvale has experimented with the magic and capabilities of summoning the fiends in the planes beyond. They became successful in gathering together several quasits that they control. Yet this was not enough, and they could summon a large glabrezu known as Kroth’latir. This creature was able to convince Uldrasir that it would be able to grant the mage more powers if they were to feed it unsuspecting souls to add to the eternal armies of the abyss. This temptation was enough to drive Uldrasir to use their quasits and own powers to gather several people to start spreading the word of Kroth’latir, souls that were now held within their control.

Plot Hook. An old ally of Uldrasir beseeches the adventurers to help their old friend escape from the hold of their obsession. Additionally, cultists of Kroth’latir are searching for a party to add their power to their roster.

Masters of the Realm (Levels 11-16)

A General’s Invasion

Creatures. This adventure features the following creatures: bone devil, horned devil, ice devil, lemure.

Premise. Under the orders of an archdevil, the ice devil known as Clanoteth was granted a sect of devils to invade the mortal realm to take more mortal souls to join their army. Clanoteth is joined by two bone devils, three-horned devils, and a large collective of lemure, all of whom act under the command of the archdevil, though Clanoteth is the leader of this invasion on the mortal plane. The devils are here to cause havoc by invading a city. This city falls under the might of the vast army of devils.

Plot Hook. A collective of resistant members wish to liberate the city from the devil’s grip, and the party is approached as close as possible to the invasion. Also, the party could be residents within the town and watch as the invasion quickly cripples the abilities of the local militia.

Masters of the World (Levels 17-20)

The Undead One’s Bargain

Creatures. This adventure features the following creatures: glabrezu, hezrou, lich, vrock.

Premise. In a search for the ancient power of lichdom, Erethod Qindal was approached by a demon prince with an offer. Erethod would receive the power that they craved. In return for such a gift, they would be indebted to this demon prince who would use them as a leader for a demonic invasion. Erethod took the offer hastily, achieving great power. Centuries later, the demon prince approached Erethod in a dream and told him that now was the time for the invasion and that he was the vessel by which the demons would expand their forces. Erethod opened a rift between the mortal realm and the demonic plane in the center of a capital city. With powerful demons pouring through, Glabrezu, Hezrou, and Vrock invaded the city streets, killing and playing with the mortals. Erethod took their place upon the throne as ruler of all in the name of the demon prince.

Plot Hook. Several groups of survivors flee from the city and head toward the powerful heroes immediately, with the hope that they will be able to stop such a powerful foe. A powerful party ally may also cast a final message to them before Erethod kills them. Erethod could call out the party, wishing to secure their place as a great and powerful being.