[@Cojemo]

Basically, my idea for the NP would be to make it kind of like an evolved form of Knight Tactics where you invite check failures by viewing her dance, which you can then exploit. It also opens up the enemy to 'critical hits'/Counters and such. Think of it as a better version of Knight Tactics but focused around dancing and used constantly.

Knight Tactics really messed up Saber in Fate/Zero, as an aside, so it's a really potent ability.

Mental interference is very easy to resist so having that as your exclusive noble phantasm would be very weak, especially in a war with so many top-servants.