From SA Mafia Wiki
An Assassin is a scum role which shrugs off roleblockings and can break doctor protects with their nightkill. This allows the mafia to kill whomever they like without worrying about the kill failing for normal circumstances, though typically the assassin will be balanced with roles that can track or watch the kill being performed. Sometimes assassin kills can be blocked by jails, or can fail against a Hider, since those roles are often phrased as making a player immune to "all night actions," thus preempting an assassin kill. Ask your mod.