On sector mode there would be a mini box next to it there is Four modes,
1) Easy ( lower drop rate and lower xp but monsters are less and are easily destroyed)
2) Normal ( Everything is just the way it is )
3) Hard ( Drop rate is slightly higher and 3 or 4 more monsters, monster has more Def,Hp and attack and you get more xp )
4) Nearly Impossible ( Drop rate is quite higher that Hard sightly more Mini-Bosses and Mobs, Monster has loads more hp,def and attack and you would get alot more xp than Normal)