Find and defeat the rare monster Gold Mecha Robo.
What you need: Loads and loads of strength, patience and magic skills,
Location: Ancient Factory - Towards the far side of the first room, near the Black Barrier.
Recommended Minimum Level: 85 minimum with really really high leveled shadows.
Strengths and Weaknesses: Strengths - Strong and good defense. Weaknesses - None. He has 18,000 health points.
I personally set all my characters to level 99 Sword Attack front row and 99 Black Magic back row. I equipped them with an array of accessories to up their stats, but maily equipped them with Skill +8, Endure, Resurrection, White & Black Magic Level 8, Double Cast and if they have a high Support level (99), use Magic Essence as well.
I got it together with another robot using the encounter circle and used that to build my party ready for it. I used Quickus on the middle of the party fully boosted, I used prerevive on everyone, and used a fully powered Regenera. Then I destroyed the party to move on to the Gold guy.
Once there, I used plenty of Waterus doubled (2 x 1,000 ish), water sword (2,500 ish) all the way through, healing inbetween when necessary. I personally completed it without losing even one character once, so, it's not tough once you are leveled up.