I just got a large ambush from a nearby faceless one civilization. More than 30 soldiers in total, and also their mounts and a few war animals.
For backstory, my military consisted of 20 men - the first squad consisted of only 3 dwarves, the rest were either Goren or Gray Cyclopes, both semi-intelligent humanoids capable of using weaponry. Was enough for the most part, as they were all training nearly the entire year round.
The full list was actually bigger as these are screencaps I took earlier on in the ambush.
I've had one ambush from them before, but nowhere near in these numbers - last time they brought two C'thrax wrestlers, who are gigantic and have pincers instead of tentacles. That said they still were relatively unprepared, and went down without causing any casualties.
They notably brought a Starspawn with them - the largest caste of the faceless ones, practically megabeast-level. This is where all two of my casualties resulted from - they can drive dwarves insane with some of their unique abilities.
Rh'nel drove one of my swordsdwarves insane, resulting in him attacking and killing one of the goren swordsmen I drafted into the military.
At that point, only a few of my soldiers were fighting Rh'nel - the others were chasing around the remaining Faceless Ones and Unbroken who were attempting to rein in their terrified mounts. This proved to be advantageous as most of the dwarves entered martial trances.
I eventually ordered the entire force to strike at the Starspawn. The combined forces managed to pierce through Rh'nel's armor and carapace enough to cause major internal injuries - the gargantuan horrors heart was torn by the assault.
Rh'nel eventually died - it appeared he left one last surprise, as one of the goren swordsmen struck down the swordsdwarf who had killed his friend in his insanity.
The remaining stragglers didn't pose much of a challenge, as their mounts were too out of control to obey their commands. Eventually none remained.
The forts exterior was covered in various shades of blood - the peasants took to the cleanup as the soldiers rested and recovered their injuries.
I ordered a specific statue made for this occassion. I placed it in the crypt, where all the dead members of the fort rest.
Mostbad endures.