You can summon HFS from the summoning pit just like any other pet, so bringing them from embark does kinda make sense.
That would make the game too easy as they'll pop up in caravan as well. I'm trating them like masterwork armor for now, rare except when you have them made because your fort is special.
Quite a few new pets. One of them was Blizzard Men for 1 point. Turns out, Blizzard Men are 95% citizens, they can do everything but be nobles. This is possibly a mite overpowered.
Keep reporting pets you see available for 1 point, they lack a defined value and should be fixed.
Well, its not just DFhack. Its the game in general that just crashes after about 5 minutes of gameplay as well. Probly DFhack related as well?
EDIT: sigh, and another Succubus fort bites the dust due to DfHack before I can even get through a year. This is agonizing that I can't seem to continue past a few months with Succubi. >.<
I'll make random guesses but mdf is indeed a lot less stable than with vanilla. Perhaps it's the higher number of creatures and stuff that make it more prone to hit a bug. So far disabling twbt and be careful of spawned creatures (do not butcher summoned animals) make it more stable.
I'm sure the system is at play, I'll run your save and see what's up.