I think what they meant is that Mammons carry debug elixirs. They look the same, but are listed seperately and can be sold at a much higher rate than the normal ones.

I haven't really battles many Nemeses myself. I got Firaja and Blizzaja (BTW, it annoys the hell out of me that they didn't register in the journal) and once battled Turtledove. I love the Ba'ali battle theme!