By accident I discovered a way to bypass the spawn door for the genji player in Mischief & Magic, and I did it again and discovered its very repeatable.
Either during the round winning kill cam, or during the time transitioning to the next round you can control the player character early before the rounds actually started. This breaks the mode because between rounds the spawn doors are unloaded, so you can simply walk or use the dash ability to exit the spawn door before it loads in. This means the genji player can completely bypass the hiding phase thus breaking the mode, so this exploit can ruin the gamemode if abused.