@KitFox Wrong Garm. You want Garm, Lord of Hellhounds. Garm of the Cave, the Prince of the Fenrir, the Firstborn of Fenris. Garm Tyrslayer, Garm of the Fangs, who is chained in Niflheim and charged with ensuring that no member of the unworthy dead escapes the punishment due to their cowardice and betrayal.
The current TMNT TV series has a similar visual cue: when its main characters are in hyper-competent ninja mode, their eyes go dead white. You can tell when something affects them strongly on a mission because their pupils snap back into place as they're shaken out of ninja mode and into teenager mode.