(edit: I should have looked for other threads of the same thing. I don’t need a response but how come i’m not allowed to delete my own post?)
I was fighting Magistrix Norroa and got the Frostmourne weapon. So I used Continuum Colider to get an extra turn to trigger the deathrattle sooner but the deathrattle did not trigger.
Long story short, the Frostmourne’s deathrattle does not trigger against Magistrix Norroa during extra turns.