A Nexus is a player that passively redirects players who target it to a random other player. Kills cannot be redirected in this way, so as to prevent the Nexus from being unkillable.
This role is very much within role madness. However, it is not necessarily of any alignment.
Nexus is the opposite of Lightning Rod.
Nexus can be given the X-Shot or Odd-Night modifier to allow it to choose which Nights it wants to have its redirection ability active. Because a Nexus modified this way can be killed on some Nights, its redirection ability may apply to kills.
Use and Power
Nexus is mostly good for adding chaos to the game. A Town-aligned Nexus is more likely to hurt Town, but a scum-aligned Nexus is more likely to help scum. As a result, there is a case to be made for policy lynching Nexus claims.
A Serial Killer that is also a Nexus is particularly strong, as it essentially cannot be detected by any means other than the lynch. (However, it is possible for the role to be accidentally incriminated via false positives caused by redirections onto players who happen to be performing scummy actions at the time.)