Draconians

 Fizban's Treasury of Dragons gives us a ton of new monsters. Many of these are new dragon types - like the major dragons in the Monster Manual, we get wyrmling, young, adult, and ancient versions of all the gem dragons, as well as a few other types.

But it's not all just dragons. One group that really fascinate me, and feel ripe to use as a major threat in a future campaign, are the Draconians.

Now, I know very little about Dragonlance as a setting, but I do think they were introduced for that setting.

Draconians are humanoid-like monstrosities that are created through the corruption of dragon eggs, producing dragon-like soldiers than have various specialties. They look very vaguely like dragonborn, but are not just normal people. The trait they all share, other than being sort of draconic in appearance, is that upon death, they explode, unleashing violent magic that can damage or debilitate the foe that struck the killing blow (and anyone else nearby).

While their alignment is listed as "any" (likely reflecting more modern sensibilities when it comes to intelligent beings - notably, I believe that even fiends like demons will in the future be listed as "typically chaotic evil" rather than as a blanket statement, allowing a DM who wants to tell a certain kind of story to produce outlier NPCs) these guys very much seem like bad, bad news.

In particular, I find the Draconian Dreadnought to have immense story potential, and might give its unique ability to others. While it's the biggest of the Draconians, and is built primarily as a melee bruiser, it can also steal the appearance of a creature it slays, and the disguise lasts indefinitely.

Draconians are mass-produced - a single dragon egg will yield multiple draconians - and their universal "Death Throes" trait marks them as, it seems, kind of disposable to their masters - a fire-and-forget weapon that will, at the very least, do some damage on the way out.

So, in my mind, the Draconians represent a hidden threat - highly dangerous monsters that are intelligent enough to infiltrate society - but even after the grand conspiracy emerges into the open, the draconians are still fearsome foes to meet on the battlefield. An evil, secret army could be building up beneath everyone's notice.

Draconians range in CR from 1/2 to 6, which means that nothing here is going to be a boss-level threat. They seem to be designed to be minions. But I could imagine that some evil dragon, perhaps plotting a return to power or some kind of conquest, might send these out as their henchmen - maybe the party encounters some bandtis who are better-armed than they ought to be, and when they fight them, it turns out their leader is actually a disguised Draconian Dreadnought - only revealed when they are struck dead and explode with fiery force.

Notably, the Death Throes ability says that it triggers when the draconian is reduced to 0 hit points - not when it dies (though the effect will surely kill it). That means that there's no knocking these guys out with nonlethal blows. Thus, you have some terrifying foot soldiers for an evil mastermind that are going to be practically impossible to get any information out of.

While I have so many campaign ideas in my head, reading through Fizban's has given me some ideas for one set in my own world that would likely center around the return of a long-dead draconic tyrant - and these monsters would be a great first sign of the threat to come.