I believe that the idea of what happened to the few hero's who went missing were probably taken prisoner and used as a reference for their fusion duplicates but then soon escaped after fuse's minions attempted to lock them away for more copies but they out smarted them and met up with tetrax and samurai jack and informed them of the things that they went through and then jack and tetrax passed the information on to dexter, blossom, mojo jojo, and double D and when as for buttercup the monsters probably used her dna as a base when they probably attempted to capture her but ace probably stopped them