Night of Hell: Fall of the Five Shires
by David KnottIn the Nightmare Dimension, the diaboli are the mostly chaotic good counterparts of the mostly lawful good humans of Mystara. However, not all inhabitants of that Dimension are so benign. In particular, the Dark Urdlings who serve Lawful Evil devils (who show the same degree of interest in the Nightmare Dimension that the Chaotic Evil demons do in the Normal Dimension) concoct a plan to invade the Normal Dimension after many plots to take over their own Dimension fail. They construct gates from their world to the Normal Dimension by focusing on areas where negative energy is concentrated -- namely, in the halfling clan artifacts known as "Crucibles of Blackflame".
The Dark Urdlings can best be described by taking the Urd race from 2E sources, converting them to 3E, and then applying the "fiendish" template. The result is powerfully nasty Lawful Evil beings of a sort never previously seen in either the Normal Dimension or their own Nightmare Dimension.
Anyway, once their gates are in place, they launch their invasion. One night, each of the hundred clanholds of the Five Shires becomes a literal "Hell on Earth" as Dark Urdlings pour through gates located very near to the most precious relics of each clans. Within minutes after the beginning of this invasion, the very land of the Five Shires is corrupted, as those few heroes who attempt to Deny the invaders burst into flame and are utterly consumed in the attempt. By dawn, most inhabitants of the Five Shires are dead or missing, and a small few manage to flee to neighbouring nations with incoherent tales of the horrors they faced that night. The Five Shires are now dominated by horrifying monsters from the Nightmare Dimension.
Of the hundred Crucibles of Blackflame held by the hundred clans of the Five Shires, 95 are seized by the invaders, while heroic adventurers manage to salvage the other five and take them to far distant locales where they can (it is hoped) be hidden from the invaders.
Halfling recovery becomes a major project in Glantri, Karameikos, NACE, and other magically inclined nations as (at the request and bribes of the refugees) they research spells to rescue halflings from the Nightmare Dimension. The rescued halflings vary as to the degree to which the Dark Urdlings managed to assimilate them into the Nightmare Dimension:
Degree 0: These halflings suffered minimal exposure to the horrors of their new dimension. As their willpower made up for the traumas that their bodies endured, they gained +2 to Wis at the expense of +2 to Con.
Degree 1: These halflings became moderately adapted to the Nightmare Dimension. In addition to the effects of Degree 0, these halflings gained the ability to detect evil, magic, or undead at will. In return, they became an "ECL + 1" race in 3E terms.
Degree 2: These halflings can all but call the Nightmare Dimension home. In addition to the effects of degree 1, these halflings gained the ability to dimension door or shadow walk three times per week. In return, they became an "ECL + 2" race in 3E terms.
Degree 3: These halflings actually can call the Nightmare Dimension home, even if they don't want to do so. In addition to the effects of degree 2, they are now classified as Outsiders native to the Nightmare Dimension and as a result gain the same immunity to magic possessed by the diaboli. In return, they become an "ECL + 3" race in 3E terms.
Note: Anyone familiar with the Birthright/Cerilia setting should recognise it as the source of the abilities gained at degrees 0-2.
Anyway, the "Night of Hell" would introduce some major changes to Mystara, especially in regard to the treatment of halflings. First off, halflings would lose their major homeland and become rarer than gnomes. Initially, player characters would be limited to refugees and expatriates who either escaped from the "Night of Hell" or were already outside the Five Shires when it occurred. In the following years, "recovered" halflings would become possible player characters, with maximum possible degree of assimilation increasing as the years pass. All "recovered" halflings would incur a debt to the wizards of whichever nation recovered them and thus automatically have the social status of indentured servants. No halfling would be able to acquire the Denial ability or become a Master after the "Night of Hell", and any Master who managed to escape from that disaster would be unable to advance further in that class (though he would be able to gain levels in prior classes in 3E terms).
As for the Dark Urdlings: After the Five Shires, their next logical target would be the Atruaghin Plateau by way of the Malpheggi Swamp, thereby stirring up another Known World nation that is a bit too peaceful at present. The Atruaghin natives would view these new intruders as evil spirits and probably find that their patron Immortals are quite willing and able to help them fight off these half-fiends. However, this would be a good time for these half-fiends to be contacted by disgruntled NACE aristocrats who do not much care for the recent changes in what remains of Alphatian society. The alliance of the Dark Urdlings with the disgruntled Alphatian wizards results in another conquest like the one described in the PWAs -- but this time the invaders are not so easily dislodged, and the best efforts of the Atruaghin natives to rebel fail to free their homeland but serve only to block the plans of the evil alliance to expand further.