Low level applies to ALL normal mode dungeons the more dungeons you unlock the more variety in roulette however keep in mind that you are more likely to get like tam-tara or copperbell or something of the like just because. Can't decide if the game is trolling me or if it specifically picks the same dungeon 3 days in a row -_-. When you get level 50 you unlock hard mode but you need to actually DO a few hard mode dungeons first.