In Curse of Strahd players will encounter
Baba Lysaga's Creeping Hut
which is tagged as a gargantuan construct.
The hut itself is a small shack placed on top/inside of a gigantic rotting tree stump/roots.
The druid in the campaign has Blight and the question is can blight effect this specific construct, or no?
Necromantic energy washes over a creature of your choice that you can see within range, draining moisture and vitality from it. The target must make a Constitution saving throw. The target takes 8d8 necrotic damage on a failed save, or half as much damage on a successful one. This spell has no effect on undead or constructs.
If you target a plant creature or a magical plant, it makes the saving throw with disadvantage, and the spell deals maximum damage to it.
Clearly the monster is tagged as a construct, so blight shouldn't work, but it's also a gigantic tree, aka plant. Most constructs tend to be rock/metal/other and it makes sense to not be able to blight a suit of armor, for example. But since the material making up and moving the construct is plant matter is there some flexibility here?