BKB grants you spell immunity which means CM's ulti that is channeling in nature will not be interrupted by certain spells. Keep in mind that certain spell can still go through BKB (Enigma's blackhole, Magnus' RP, Pudge's dismember, Bane's grip, Lich's chain frost, etc alot more.) If you happen to play against a Silencer, you have to be patient before using your BKB charge. Either you use BKB too early and get silenced while in BKB state or you wait till global silence is used then you can BKB to break the silence.

As for NP, you can easily solo him once you get a Dagger. Just wait for him to rat and make sure he's alone in that lane. Blink in don't immediately use frostbite. Just casual nova and hit until when he is in mid TP animation that's when you frostbite and ulti.

I personally don't like CM as a hero that much lol. Too slow, too squishy and can't be in the front line initiating..

This is a game I played with our fellow lyn members yesterday: http://www.dotabuff.com/matches/1178661046
Thanks to the loud Silencer, I can roughly estimate their ward positions lol. Gank mid early and went on farming for early blink. Made opponents to be scared and stick as five always.. That opens up the map for our cores to farm.