Dodge Master: Miriam Achievement 「Rabi-Ribi」
As the game's resident store clerk, Miriam's gimmick is she will use your items against you. She has the innate ability Badge Copy which will give her various stat boosts depending on what badges you have equipped. You can sabotage her by carefully choosing which badges you use, most importantly letting you reduce her defense. In addition to Miru's multitude of buffs, this lets you go into the fight with a huge advantage.
This build emphasizes Erina's attack, which in combination with the badges listed below will reduce Miriam's defense. Entering the fight with low HP and using the carrot shooter makes Erina a very powerful glass canon, which is fine since the goal is to not get hit anyway. This trivializes one of the toughest bosses in the game and makes beating her one of the easiest achievements to get. You don't have to dodge much when you never give her the chance to attack in the first place :)
Important Badges Used + Effects:
Crisis Boost - Erina: +25% ATK when HP is less than 20% ; Miriam: no effect
ATK Grow - Erina: ATK damage output increased ; Miriam: ATK up, DEF down
ATK Trade - Erina: ATK +25%, Damage taken +50% ; Miriam: ATK up, DEF down
Arm Strength - Erina: Hammer attack +15% ; Miriam: no effect
Weaken, Self-Defense, Frame Cancel, Stamina Plus, Blessed, Hitbox Down, Survival, Top Form, Tough Skin, Erina Badge, and Auto Trigger all grant benefits to Erina but have no effect on Miriam. Carrot Boost would increase bomb damage by 10% and also have no effect on Miriam, I just didn't use it here. Just be sure NOT to equip Pure Love, as that will give her the Bunny Lover ability which reduces her damage taken by half.
Difficulty: Normal (Standard)