The Mourner trousers are part of the mourner set. To obtain them, players must kill a level Mourner on the path to Prifddinas. However, the Mourner will bring all combat stats down to 20, so it is recommended players bring a stat restore potion before fighting. The damaged trousers will need to be repaired to be of any use.
When the player first obtains the trousers they are damaged and must be repaired. Players need to take 2 silks and a bear fur to Oronwen, the Elven Seamstress in Lletya, to have the trousers repaired. She requires around 2 minutes for each set of trousers you wish to repair.
If you already have a full mourner's set you can enter the Mourner's headquarters and go to the basement and kill a level 122 Mourner to get another Mourner's set, including a pair of trousers that will not need to be repaired.
After completion of Plague's End, the mourner gear may be reclaimed from the mourner headquarters in West Ardougne. To obtain, enter the headquarters and descend the trapdoor. In the south western room is a chest from which the gear may be reclaimed.