What level should i goto the dark world?

right now i have either:

4 onion knights, 2 onion swords each + full onion equpment levels 56 56 58 58

or

3 ninja w/ full crystal equipment + 55 shuriken(man that was a long time to make money haha) levels 56 56 58 plus all those other "forbidden" weapons
1 sage w/ whatever you tell me what to put on it i will, level 58, btw what spells should i get?

Also, how do you beat the cloud of darkness? i was just messing around and went at him with the onion kids at like level 50 for all of them with 2 onion swords each and i never hit it once.