COMB in ADJ (用于 bullet,fire 等名词后构成形容词)表示“留下…伤痕的”,“被…损坏的” -scarred is used after nouns such as 'bullet' and 'fire' to form adjectives which indicate that something has been damaged or marked by the thing mentioned.
...a bullet-scarred bus. 弹痕累累的公共汽车
...a lightning-scarred tree. 遭雷击的树
COMB in ADJ-GRADED (用于battle 或 drug 等名词后构成形容词)表示“留下…创伤的” -scarred is used after nouns such as 'battle' or 'drug' to form adjectives which indicate that the thing mentioned has had a permanent effect on someone's mind.