Yesterday I was playing mission 7 of the Zerg (Episode VI) campaign of StarCraft Brood War. You're not allowed to build Guardians there, so I had to rely on Duran (an infested Terran Ghost) and Queens to get rid of tougher enemy units.
When opposed with a (Dark or normal) Archon, I noticed I couldn't use the Queen's "Spawn Broodling" ability; the system says it can only be used on non-robotical ground units. However, when I tried to use Duran's "Lockdown" ability on it, the system told me that it can only target mechanical units.
How can a unit be robotical but not mechanical? Or is the Archon somehow a non-ground unit, even though it "walks"?
Best Answer
At a guess, Archons are immune to both abilities as being purely mental beings. They are not mechanical (unlike Reavers and Probes), but they are not biological anymore either.
Here's what Blizzard has to say (Starcraft II but should be the same as the original in this aspect):
and later
Note that they are described as merged souls, "Protoss spirits", formed by laying down the lives of two warriors. They are certainly not mechanical. They form by two warriors merging on the battlefield. They are not built (as Reavers and Probes are). But it seems that the merging process only involves their souls/spirits. It leaves the biological bodies behind. They end up as pure psionic creatures. As such, there is nothing for the broodling to infest.
I believe that Archons and Dark Archons are unique in this aspect. Every other Protoss unit is either mechanical, biological, or both (e.g. Dragoons).
The reason why it doesn't work is just being reported incorrectly. The Archon is a non-robotic ground unit. It just doesn't have a biological component that is vulnerable to broodlings.
I find this explanation more consistent than trying to shoehorn the Archon into being a non-mechanical robot, even though it directly contradicts the error message. The message is simply wrong.