Ok if you read my last post heres the update.. 2 more missions here and 2 more mask with a rogue as one of the classes. So it was coincidence that the time I got the dagger was the time I used a rogue in the mission. DUN DUN DUN GOOD LUCK ALL seems to be about a 1 in 6 ratio from what I have heard and read. Does not matter which classes you choose.
3 boxed the mission 6 times before I got the dagger. I am not positive but you might to need have one of the classes a rogue to aquire the dagger. It could be coincidental but I had boxed : warrior, cleric, & a caster everytime till the 6th time and I picked a rogue and viola! The rogue was a better box with the tank and cleric I found out anyhow. The casters except the necro are very low damage in this mission. DONT PLAY A WIZARD. THEY SUXORS.