So, Umineko witches are way-overpowered and basically reality-warpers. Bern can do pretty much whatever she wants with her magic, nonsensical or otherwise, but her chief ability is miracle-manipulation. Described in canon, she is able to make an event happen as long as it doesn't have a zero-percent chance of occurring in the first place. Even if there's only a 0.00000000000001% chance, she would be able to make it happen. These powers do not work on the Tower admins, but may work on the PC characters with varying degrees of effect.

However, her powers can be negated by anti-magic abilities or weapons, and she is less effective against those who do not believe in magic at all.

Drop a comment here if you'd like to not be affected by Bern's powers, or some specific part of them, or if your character wields some hefty anti-magic power, etc.