I love this idea, and might just have to steal it !

I reckon you could make a whole adventure out of it; a seemingly endless series of iterative upgrades, each one nerfing a specific advantage of the party. Mage doing too many buffs ? The construct's weapons apply a Dispel Magic to a character when they hit. Invisible characters ? The constructs puff out clouds of glitter each round. And so forth, one upgrade at a time until the party start to feel doomed....