Time for another installment in the occasional "Trick Monster" series of monsters.
Some monsters have a limited-shot attack that is substantially better than normal. Their baseline attack might be strong enough, but their limited-shot attack will be much more powerful. Generally such an attack will have 1-5 uses. More than that and it's just an attack to be parsed out over a fight as needed. The lower the number of those attacks, the more like "trick" it will feel.
AD&D Dragons are a classic example of this "trick monster" - they have a 3-shot high-damage breath weapon (at least the evil ones do.) From my own Felltower campaign the Lord of Spite falls into this category (along with others) - he has a shout attack that he can't deploy that often, seemingly once per combat, but it's especially devastating.
Monsters which generally have a single ranged attack - a thrown weapon, say, or a crossbow they don't tend to reload - don't quite fit the bill. Nor do ones that have an attack with a cooldown or a pool of energy that can be deployed for other things. It's more like a low-maximum-use attack that does something out of the ordinary for the creature.
The fun of deploying these, to me, is that there is a short window in which you can kill or incapacitate them before they launch their best attack. After that, they're reduced threats. Do you let them get off the "nuke" and then leave them aside? Do you try to get them to run out their attacks in a wasteful manner, such as goading a dragon into breathing onto a well-protected isolated target to spare the rest of the group the damage? It makes for an interesting tactical choice once the PCs recognize these creatures for what they are.
I personally need to put a few more of these in to my campaign . . .