You know, after completing the WHOLE monster kill list, (specially the 500 coal sprites!), it just feels a bit anticlimactic that nothing else happens aside from the individual rewards. Wouldn't it be nice that after killing all those monsters, the list was substituted with a Hall of Fame type portrait of your character? I think it would be well earned! (crappy example below)
I think it'd be funny if a protest occurs from some monster advocating PETA types to chastise you for killing everything in the mines. It could be some kind of stupid event.