Thunder Squadron Engineer (tweak of the 5e Artillerist of the Artificer class)
by Marc SaindonStarting from a quick article in the vaults of pandius (see below) and my own knowledge of chinese history, it's clear that there is a potential to add "silk-punk" technologies in Mystara without derailing its medieval setting (we've got Serraine and the Savage Coast for that). So yes, the Ochalean army might have a few elite squads of engineers that can master the equivalent of gunpowder for both offensive and utility.
Naturally, Mystara doesn't have gunpowder. The equivalent it gets is the very expensive smokepowder that is only found the cursed Savage Coast, imported at a much higher price. However, it is possible that Minrothad traded some with Ochalea in the past, and the officials at the Ministry of Wonders (the magic bureaucracy) got its alchemists working on a low-cost substitute at the Hall of Worthies (my fan-made magical school). The result was Thunderpowder, a weaker form of smokepowder, and the earliest success was in creating minor pyrotechnics known as "thundercrackers" (a nod to Transformers), which are like our firecrackers, but more expensive.
The alchemists couldn't quite reverse-engineer the firearms of the Savage Coast, lacking rifling and gunsmithing techniques, as well the properties of the thunderpowder. However, instead of expelling a bullet from a tube, they would just propel that tube as a rocket, which could become quite complex multi-stage explosives.
The Ochalean army has recently cross-trained some alchemists and engineers as a new squadrons (which is why they are not in the almanachs), making the new subclass available as PCs. They might be sent on missions to field test different weaponry. Ochalean officer seem to appreciate the Thunder Squadron, as despite being glass canons, they respond well to orders and to rewards, and don't have the egos of Wizards. The Thunder Squadron uses rockets and grenades, not the Eldritch canon or Arcane Firearm of the 5e Artillerists.
Rockets should misfire at random times, as the technology is not stable. A D20 roll with the result of 1 results as spell damage to the caster (so a 'Homing Rocket' gives Magic Missile damage to the caster). A multi-stage rocket could contain more than one spell: up to 20 levels in spells, limited by the caster's own level, so a level 10 Artificer could stack one magic missile and 3 fireballs. the level of each additional spell adds to the misfire risk, so the 3 additional fireballs bring the risk of misfire at 10 on a 20, a 50% chance of disaster that might be required when facing a truly desperate situation. As a Feat, "Safe Spell" might be invented to make the inclusion of an additional spell safe, so if you purchase "Fireball", you can stack it up to the maximum without increasing the misfire factor. (A lot of this is still brainstorming). Non-lethal rockets are possible, so you might have "Web" grenades and rockets.
Thunder Squads don't have an animal motif, as they are new, not well-known, and the main thing people remember about them is the loud "boom!" that accompanies them.
(Image from: https://humankind-encyclopedia.games2gether.com/en-us/warfare/game-content/units/Unit_LandUnit_Era4_MingChina_RocketCarts)