A large portion of relevant modules/templates have now been switched to cargo. Various usages of SMW throughout the wiki need to be replaced by the new functions, in particular item tables. If some pages do not show up but contain no errors, please null-edit them. To see how you can help with the port check out Path_of_Exile_Wiki:To-do_list/SMW_migration (and leave a comment on the talk page if you have questions).
Headsman is a notable Ascendancy passive skill for the Slayer that grants damage reduction against reflected physical damage. It also grants more damage and increased area of effect of skills if you have killed recently.