What was it that Rido did to the Night Class?
It's been a long time since I've seen the anime but I vaguely remember Rido's unique power having something to do with some kind of poison effect. Its not literally poison, but a slow, painful draw on one's life-force. If I'm right, then that's definitely not what happened in the scene with the night class. I think it's related to Rido being a pure-blooded vampire, but a little more in depth to his specific family line. This is what really makes him a unique character. Surely if these questions are ever firmly answered, it will only be with further questions.