Those are all great suggestions.
Having only dipped into reading CW, I'm not familiar with the trollhound (beyond it's being monstrous). But one thing that springs to mind is (if it fits) having some kind of greater trollhound(s) show up at some point, and seriously impact the creatures' loyalties. Suppose the greater versions have some kind of innate sway with creatures of like kind. Maybe the companions would turn on their masters, so the PCs have to fight the greater trollhound(s), while suffering the bites and scratches of their companions (because they surely wouldn't attack the creatures they've nurtured and relied on!). And if the PCs kill the greaters, how do the companions react...?
And so as not to make this a gratuitous "I'm trying to take your animals/familiars away from you because they unbalance things" type moment, set it up so that the effect the greater 'hounds are having on the companions is very clear before there is any face off. Maybe some howling in the distance for a couple nights, that the trollhounds among the party react to in a distinctive way, a way in which handle animal and/or survival checks can interpret....
Just two cents off the top of my head.
(How did that get there?)
Gnome Boy (a.k.a. "Jon") • DCC play-tester @ DDC 35, Feb 2011. • Beta DL 2111, 7:00 AM PT, 8 June 11.
Playing RPGs since 1977 • Quasi-occasional member of the Legion of 8th-Level Fighters - Holds the power to play gnomes at will!
Here Be DCC Monsters...
Pbp Secret of Bone Hill characters:
Flavia, WAR, Beekeeper, L, Str 10, Agi 10, Stm 7, Per 10, Int 12, Lck 7, AC 10 hp 5, staff, jar of honey, 10-ft pole, 1 pc chalk, 50' rope, 2 torches (1 lit)
Hector, DWARF Apothecarist, L, Str 5, Agi 11, Stm 12, Per 10, Int 6, Lck 10, AC 10, hp 11, sword, shield, cudgel, steel vial, chest, flint & steel, empty flask, lg sack
Chendris, WIZ, Alchemist, N, Str 11, Agi 9, Stm 12, Per 15, Int 13, Lck 15, AC 10, hp 3, staff, empty flask, 50' rope, 2 candles, lg sack, oil (1 flsk), 1 torch, snakeskin tome; speaks gnoll
Darrow, CLR, Hunter, N, Str 11, Agi 12, Stm 8, Per 16, Int 7, Lck 12, AC 10 hp 5, short bow, 6 arrow, 10-ft pole, deer pelt, torch (lit)