I use my FWW+PB Najasaurus for AoEing down the spawn at Champs. He's excellent for that. I also use him to tank all the spawn in Paroxysmus' Palace as i gather keys with my Thrower.
I'll go down there on my Disco/Tamer with my FWW+PB Najasaurus and stuff them in a corner while running Consume Damage on the Naja, and then i'll run around on my Thrower gathering up all the Poison Eles/Acid Eles/Plague Beasts just before the Poison Trap area with the demons. I'll lure that spawn to my Najasaurus, invis my Thrower, and discord the spawn as they surround my Najasaurus. With Consume Damage running, my Najasaurus out regens their damage output on him, they can't kill him. I then run around on my Thrower killing all the Corrosive Slimes for body parts. Makes farming Paroxy Keys ALOT easier (although it still takes awhile to get several complete sets).
My Najasaurus can also be used to tank the Putrifier as my Thrower attacks the Putrifier from max range (to avoid his Poison Breath and re-targeting). With 80/80/45/100/60 Resists and Consume Damage running, almost nothing in the Palace of Paroxysmus can kill my Najasaurus (i don't use him on Paroxy though, he'll insta kill any pet). Even the Putrifier can't scratch my Naja with Consume Damage running.