I've killed fradubio a few times (its hardly worth it) ive never seen more than 3 duessa at once. I had a 75ninja steal my claim on fradubio once while i was killing the duessa. He was good enough to take the main NM but once these popped up he died fast. They are tough enough to take down blinks off a lvl 75. If you must have the cape from this NM get a friend or 2 to help you clear the saplings to avoid losing claim or death.
Other info they didn't put up.. -It IS "Impossible to Gauge!" -It is spawned by Fradubio. First it spawns one, and if you kill the one it spawns 3 the next time, and I dunno how many after that, I wasn't high enough to help a whole lot and we had to give up.