The most USELESS monster.

do they (troglodytes) not have immunity to petrification? Because it never worked for me...

It doesn't seem like they have that trait. It's probably just a trick of the Great and Terrible Random. Because of it, I rarely use minotaurs. Medusas shoot constantly, but a mediocre melee unit with an ability that supposedly works once a year is easy enough to find. And even when I fight minotaurs, their ability will ALWAYS activate in 80% of cases instead of the promised 30% (or whatever it is, I don't remember anymore). So, for me, minotaurs are one of the most annoying units. However, I have nothing against their appearance.
I generally ignore pirates, zombies, troglodytes, and other similar fantastical creatures.