Hi all
Im reading David Dalglish books and on two occasions so far ive come across a summoned beast, size of a horse looking like a lion, insanely fast, hide as stone, able to breathe fire. Its summoned with a human sacrifice to Karak.

Im planning on summoning a pack of these to a group of lvl 19-20 chars. And I want them to be sort of a challenge or at least drain them of some resources.

I was thinking about mixing the Rakshasa (without innate spellcasting), with hellhound (packtactics and firebreath), and perhaps some kind of golem traits.

Any of you guys have ideas what to pick, and how to rate one, let alone 6 of these against 5lvl 19-20 chars?