So I'm fighting this intelligent lobster riding in a mechanical spider chair, see, and I'd like to knock out the chair (or at least render it incapable of moving) so I dump my successes into reducing adroitness, declaring that I'm slashing hydraulic hoses and whatnot. Thing is, at least as we could find in the rules, bringing an attribute down to zero doesn't seem to have any negative impact. Should it?

Wilhelm,

Good question. Donjon, being a weird variant of whatever it is we were playing as kids, sometimes has a problem with assumed rules. If you look at some creatures from the sample adventure, or from Donjon Pak B1, you'll see some attributes at 0, and an associated effect. For example, the Sporecaps have an Adroitness of 0, and cannot move.

Now, a lowered Adroitness is it's own punishment, but I as a GM would rule that:

Adroitness 0 equals no movement
Virility 0 equals no power to effect the world physically
Discernment 0 equals no ability to focus on anything
Cerebrality 0 equals only instinctual thought
Sociality 0 equals getting kicked out of wherever you are real quick-like

Being that this is an assumed rule, mix for your own taste.

There's also mention that if a PC is at 0 Flesh Wounds then adversaries can damage their attributes without using a damage success to detail that they're damaging attributes.

That's not the same as what you were talking about, but it is an effect of having a 0 rating.

I decided that a lowering of Adroitness in combat would remove a corresponding number of actions in a flurry due to a lowering of Initiative, too. I'd start pulling actions from the next one the character in question would be normally taking during that flurry and if they ran out of actions during that flurry, they just wouldn't have any more actions that flurry. They could actively defend, losing actions later, of course, if they still had a positive Adroitness.

Example: Goblin bashes PC for 4 damage successes, details with 1 that they bust a PC's kneecaps, thereby damaging the PC's Adroitness. The PC's Adroitness takes 3 damage, leaving them at 2 Adroitness (it's a speedy combat monster PC). The PC already took an action this flurry and had 4 remaining actions at the time that the damage took place, they lose the next 3 initiative rolls and will go next on their last initiative roll as a result of the reduction.

In other words, losing Adroitness really sucks in my game. Does that seem fair?

I hadn't thought about it before, but lost Virility could cause issues if the Virility goes below the Weight of armor or weapons, too, as per p. 22 in the "print" version of the rules.