I have quite a progressed account and am 1 keying nightmare and using rest of keys in ulitmate nightmare clan boss, but I still havent done much progression in the question because I can't fuse Rhazin for it. 

I have pulled countless blue shards and still missing Slitherbrute!, the rest of the fusion is sitting in my vault just waiting for the day! but with the rare pool getting ever bigger the chances of getting the needed rare is really slim. At least with some of the other champs I can farm campaign but that isnt the case for all.