It is possible to fear lock static bossess like Idol of Ruin, or Lagon using Spirit Plague. The fear is applied and then they do not perform any other animation and just become a punching bag.
This also works when there are static mechanics in boss fights like Abyssal Harton when the idols appear, they then become fear locked, the God Hunter Argentus fight with the balistas on the sides they can also be perma feared.
