Dark dungeon rewards

Hi, I'm lvl 9 in dark dungeon mode, what is the point of that levels, does rewards get better or something, when entering mode it says "acquire dark sword" what does that mean? Thanks!

Bro in dark. Dungeon you will get those items which you normally get in stages as drop .Sometimes you stumble upon a level called frozen castle of death that level is difficult than others there enemy are bigger and stronger at last you will found a boss called ice dragon after killing him you can get a dark sword or power stone any one of them will acquire as drop .