Savage Trollspawn gets +1 for each damaged character the engaged player controls.

Shadow: Attacking enemy gets +1 for each damaged character the defending player controls.

For each excess point of combat damage dealt by Cruel Mountain-troll (damage that is dealt beyond the remaining hit points of the character damaged by its attack) you must remove 1 progress from each quest card in play.

Trolls were abroad, no longer dull–witted, but cunning...
–The Fellowship of the Ring

Ruthless Hill-troll gets +2 and +2 while it has 3 or more damage on it.

Shadow: Shuffle 1 location with the safe keyword (but not its attached encounter) back into the encounter deck.

You cannot travel to a safe location while Scavenging Stone-troll has no damage on it.

While Scavenging Stone-troll is in the staging area, cards in each player's discard pule cannot leave that discard pile.