Trolls regenerate so quickly by incorporating the bones, muscles, and structures of the creatures they consume, so trolls are shambling, misshapen masses with too many joints, limbs that move at strange angles, and claws made of broken bones from creatures they have eaten. I described a troll like this to my players, and it made it a memorable and disgusting encounter, especially when the troll grew a new hand made out of the bones of a guard it ate.