I dont have a video for this but it has happened multiple times. Ultimate Deathknight appears with no health but will not die in arena. from what I can tell it happens when the Didn't need 'em passive is blocked and the reduce of health would kill ultimate deathknight. if its needed it happens specifically with ronda's Phase Rushdown as im not as a high enough level to face any other block passive skills yet. I have never made one of these so if your missing any information please feel free to message me. I hope this helped.