This is a one time visit, make sure to farm Bestiary. Here is the bestiary checklist:

•  Centaur Knight
• Sorceress
• Purple Bavarois
• Gremlin
• Black Knight
• Frostbeast
• Ice Lizard
• Fell Turtle
• Marionetteer (First Floor)
• Marionette (First Floor)
• Soldieress
• Flamehound

Bosses: Sisters (Sandy, Cindy, Mindy)
Just kill them in this order: Cindy, Sandy, and Mindy

Augments:

• Give Dualcast to Rosa and assign to her ability slot immediately; it allows you to cast magic twice. 
• Give Recall and Last Stand to Yang.
• This one is up to you, but I recommend give Cry to Kain.

Boss: Barbariccia 
You cannot hit her when she is in Tornado state, ONLY Kain can break it by using Jump.

Exit Baron castle.