The Garment Grid is called The End. It Breaks HP and Damage Limit and gives you access to a special ability called Finale which does heavy damage and does 99999 damage if you’ve never escaped from a battle. Fortunately, the escape counter resets with each New Game Plus, so if you actually get this, this Garment Grid is a great way to breeze through future playthroughs.
The Black Element is easily beatible if you have the Songstress’ Magical Masque or use any of the standard tricks such as Cat Nip / Trigger Happy or CONGRATS! It reappears in the later cloisters of the Via Infinito, along with most of the other tougher bosses.